sql: fix placeholder type resolution

When assignment casts for inserts were add in cockroachdb#70722, type resolution of
placeholders in prepared statements was changed so that during the
prepare phase the optimizer would only plan assignment casts when it
could not be guaranteed that an insert column would be an identical type
to the target column. Unfortunately, the change to placeholder type
resolution change strays from Postgres's behavior and breaks some
third-party tools. This commit reverts the type resolution changes, and
as a result, assignment casts are always planned to convert each insert
column to its target column type, even if the cast ends up being a no-op
because the types are identical.

I attempted to implement a solution that did not plan assignment casts
in all cases, but it proved to be tedious and error prone, so I opted
for this simpler solution for now. My attempt required annotating each
placeholder expression in the memo with a context: a non-assignment
context or an assignment context. This context would be used during
the EXECUTE to determine whether a placeholder value should undergo a
regular cast or an assignment cast: a critical decision due to their
slightly different behaviors (see `PerformAssignmentCast`). The
problem is that correctly annotating placeholders in complex mutations
with expressions like subqueries or CTEs is difficult.

Fixes cockroachdb#71576

There is no release note because this bug was never present in a
release.

Release note: None

pkg/sql/opt/exec/execbuilder/testdata/explain

@@ -793,8 +793,8 @@ vectorized: true
   into: t(k, v)
   auto commit
   size: 2 columns, 1 row
-  row 0, expr 0: (1)[int]
-  row 0, expr 1: (2)[int]
+  row 0, expr 0: (crdb_internal.assignment_cast((1)[int], ((NULL)[unknown]::INT8)[int]))[int]
+  row 0, expr 1: (crdb_internal.assignment_cast((2)[int], ((NULL)[unknown]::INT8)[int]))[int]
 
 query T
 EXPLAIN (TYPES) SELECT 42 AS a
@@ -1408,20 +1408,26 @@ vectorized: true
 │ auto commit
 │ arbiter indexes: u_pkey, u_v_key
 │
-└── • lookup join (anti)
-    │ table: u@u_v_key
-    │ equality: (column2) = (v)
-    │ equality cols are key
+└── • distinct
+    │ distinct on: column2
+    │ nulls are distinct
     │
-    └── • cross join (anti)
-        │
-        ├── • values
-        │     size: 2 columns, 1 row
+    └── • distinct
+        │ distinct on: column1
+        │ nulls are distinct
         │
-        └── • scan
-              missing stats
-              table: u@u_pkey
-              spans: [/1 - /1]
+        └── • lookup join (anti)
+            │ table: u@u_pkey
+            │ equality: (column1) = (k)
+            │ equality cols are key
+            │
+            └── • lookup join (anti)
+                │ table: u@u_v_key
+                │ equality: (column2) = (v)
+                │ equality cols are key
+                │
+                └── • values
+                      size: 2 columns, 1 row
 
 # Make sure EXPLAIN (VERBOSE) works when there is a constrained scan of a
 # virtual table (#58193).
@@ -1560,9 +1566,14 @@ EXPLAIN INSERT INTO t2 SELECT x FROM t2 WHERE false
 distribution: local
 vectorized: true
 ·
-• insert fast path
-  into: t2(x)
-  auto commit
+• insert
+│ into: t2(x)
+│ auto commit
+│
+└── • render
+    │ estimated row count: 0
+    │
+    └── • norows
 
 statement ok
 PREPARE prep AS SELECT $1 + 1

pkg/sql/opt/exec/execbuilder/testdata/explain_analyze_plans

@@ -351,11 +351,17 @@ regions: <hidden>
 │   └── • buffer
 │       │ label: buffer 1
 │       │
-│       └── • values
-│             nodes: <hidden>
-│             regions: <hidden>
-│             actual row count: 1
-│             size: 2 columns, 1 row
+│       └── • render
+│           │ nodes: <hidden>
+│           │ regions: <hidden>
+│           │ actual row count: 1
+│           │ estimated row count: 1
+│           │
+│           └── • values
+│                 nodes: <hidden>
+│                 regions: <hidden>
+│                 actual row count: 1
+│                 size: 1 column, 1 row
 │
 ├── • subquery
 │   │ id: @S1
@@ -414,5 +420,5 @@ regions: <hidden>
                       label: buffer 1
 ·
 Diagram 1 (subquery): https://cockroachdb.github.io/distsqlplan/decode.html#eJysUtFq20oQfb9fMcyTDRssOVwo-5Q0uGDiyMV2DKWYsF4NyhJpV90d1XaNP6s_0C8rlqw2IsRtaR_nzJzZM2fPHsOnHCWOk_lotoBxspiCfjR5Csvryf1oDr1YQG8-moxuFlAY2yv78G42vYNSebLc76NA61JKVEEB5UeMUeD_uBJYeqcpBOeP8L4eGqdblJFAY8uKj_BKoHaeUO6RDeeEEhN34crBEAWmxMrk9VLakq7YOAtsCpIQffsaUOBasX6kAK7ismIJEQr0bvMTiHF1ENhUp_cCq4xQXh7EM03xeU0Ltc5pRiolP4i6yhobrkpvCuV3KHBeKhskXKDAiSkMw9GQ22VX-O0StLNM9uVNt0uoT_CkUtmS1zumFnoDb1Hg3fLmBgJTCdpVlqFHWx4Yy30JUa2xGSB6em2gUFsoqHB-ByrPnVZMqYSo3v4XxsZ_Yux1lnnKFDs_iLu-XicfHpLp4iG5n0x6V_ExZv8-BMOO1l8Ec0ahdDZQR-drm6PDSiClGTXhD67ymt57p-tnmnJa82ogpcBN97IpxrZpHQU-J8dnycPz5OFZctQl16fUV6El3jj_BLlisnr3w_kW3yjD3T9JKZA3Kjdf1MsPa2mnmGsyn-kU9bbV5r3tNZlvuwWFoLLOQPS7QVgd_vseAAD___Xaogg=
-Diagram 2 (main-query): https://cockroachdb.github.io/distsqlplan/decode.html#eJyskcFq8zAQhO__Uyx7SkAQK0ed8lNcMKRxSdJeig-uvCQCRXKlVRsIfqy-QJ-s2C60KbQQ6HFmZ0Yf6ITxyaLCYrXJ11soVtsS9N7YBu7_L-_yDUykgMkmX-ZXWzgYN2mncL0ub6CtAzmeTlGg8w2t6gNFVA8osRLYBq8pRh966zQEiuaIKhNoXJu4tyuB2gdCdUI2bAkVWq9rC8-1TRQhm2UosCGujR2Wy8QKFnOxkCiQjqQTG--AzYEUZG-vEQU-1qz3FMEnbvt4PxH8y6chseoEjuqDInK9I1SyE5eSap8cg5zJc9C_Z5tfwram2HoX6Qzqp-WsqwRSs6Pxp6JPQdNt8Hp4ZpTl0BuMhiKPVzmKwo2nHvBrWf5ann8rV92_9wAAAP__OpjUsw==
+Diagram 2 (main-query): https://cockroachdb.github.io/distsqlplan/decode.html#eJysktGK1TAQhu99imGuTiG4zV5JrhSpUKg90tP1RsqSTYazgTSpyVQXDn0sX8Ank7aCu4LKgnf5_5l_8mXIBfNnjwrr9lR1PdRtfwRz77yFj2-am-oEByngcKqa6m0PowuHqYB33fE9TDpR4KJAgSFaavVIGdUnlDgInFI0lHNMq3XZGmr7gKoU6MI082oPAk1MhOqC7NgTKvTRaA9ftJ8pQ3lVokBLrJ3fJncULCUFJtm7WxeYUtD-pc7ZncNIgW-NznyQSqm67V-J9qZp9mMh_pF5LR93o0B6IDOziwHYjaSg_P4to8A7zeaeMsSZp5kVrIApfv1lSBwWgbv6-cbM-kyo5CKeuwcT58Agr-TTNfx_tuvnsHWUpxgyPYH60-RyGQSSPdP-D3Kck6EPKZrtml0et9xmWMq8V-Uu6rCXVsDHYfnX8PVv4WF58SMAAP__iA_1uQ==
 Diagram 3 (postquery): https://cockroachdb.github.io/distsqlplan/decode.html#eJy0lMGO2jAQhu99itGcQLJEAnuofNrtipWyZJMKslwqDsYZdt0Ndmo7KgjxWH2BPlmVmFVLV6BStTfm9_zjb_it7NB9qZBjks3G0wKSrMhBPquqhPlN-jieQS9m0JuN0_FtAWule3Uf7qb5A9TCkvb9PjLUpqRMrMkh_4QxLhjW1khyzthW2nUNSblBHjFUum58Ky8YSmMJ-Q698hUhx8pIUYGTQsOyWa3IQjSIkGFJXqiqG583nsP1EBnShmTjldHg1Zo4RN-_OWS4FF4-kwPT-Lrtbf3WfP0pxLjYMwzVgcN58UTI4z37c9Y7VXmyZAfxMWDQOVzHkMwgywvIHtP0v_AOL-G9N0pPSZRkB8Nj4mJbE4d0fFfATVYkcJ8nGTIMAV_XVq2F3SLD1JiXpobPRmkwut0Q2SGP9ld3ObToLfNr7byoquONJ_M3tTTak37750zm3UCwJMowdTKH5dbTq_QePiDDh_ntLThPNUjTaA892viB0r7PDw8oNBC9nGr423Cik-GMLgknPHyy1lhQq7BzPBgd5_TvGa8uYZySq412dAR1anK0XzCk8onCB8CZxkr6aI3srgll3vk6oSTnw2kcikSHoxbwV3N81jw8bx6eNY_Om0dnzVe_mRf7dz8CAAD__4iLwK8=