opt: fix BPCHAR type and CASE typing

This commit addresses inconsistencies from Postgres' behavior. First, it
makes the `BPCHAR` type distinct from `CHAR`. The former is a
blank-padded character type with no type width, meaning that it could
have any length. The latter is a blank-padded character type with a type
width of exactly 1 - it is essentially an alias of `CHAR(1)`.
Previously, a column of type `BPCHAR` behaved the same as a column of
type `CHAR(1)` - it enforced a length limit of 1.

Second, the typing of `CASE` and `CASE`-like expressions has been fixed.
The branches of these conditionals is no longer forced to have the same
type-width.

Fixes cockroachdb#127889
Fixes cockroachdb#108360

Release note (bug fix): A bug has been fixed that caused incorrect
evaluation of `CASE`, `COALESCE`, and `IF` expressions with branches
producing fixed-width string-like types, such as `CHAR`. In addition,
the `BPCHAR` type has been fixed so that it no longer incorrectly
imposes a length limit of 1.

pkg/sql/logictest/testdata/logic_test/bpchar

@@ -0,0 +1,27 @@
+query T
+SELECT 'foo'::BPCHAR
+----
+foo
+
+statement ok
+CREATE TABLE t (c BPCHAR PRIMARY KEY, FAMILY (c))
+
+statement ok
+INSERT INTO t VALUES ('foo'), ('ba'), ('c'), ('foobarbaz')
+
+query T rowsort
+SELECT c FROM t
+----
+foo
+ba
+c
+foobarbaz
+
+query T
+SELECT create_statement FROM [SHOW CREATE TABLE t]
+----
+CREATE TABLE public.t (
+  c BPCHAR NOT NULL,
+  CONSTRAINT t_pkey PRIMARY KEY (c ASC),
+  FAMILY fam_0_c (c)
+)

pkg/sql/logictest/testdata/logic_test/case

@@ -0,0 +1,47 @@
+# LogicTest: local
+
+# Regression test for #127889. CASE-like expressions should not impose type
+# widths of one branch on other branches.
+subtest regression_127889
+
+query T
+SELECT CASE WHEN true THEN 'foo'::TEXT ELSE 'b'::CHAR END
+----
+foo
+
+query T
+SELECT COALESCE(NULL::CHAR, 'bar'::CHAR(2))
+----
+ba
+
+query T
+SELECT IF(false, 'foo'::CHAR, 'bar'::CHAR(2))
+----
+ba
+
+query T
+SELECT CASE WHEN false THEN 'b'::CHAR ELSE 'foo'::TEXT END
+----
+foo
+
+query T
+SELECT (CASE WHEN false THEN 'b'::CHAR ELSE 'foo'::TEXT END)::CHAR
+----
+f
+
+query T
+SELECT (CASE WHEN false THEN 'b'::CHAR ELSE 'foo'::TEXT END)::BPCHAR
+----
+foo
+
+query R
+SELECT CASE WHEN true THEN 1.2345::DECIMAL(5, 4) ELSE NULL::DECIMAL(10, 2) END
+----
+1.2345
+
+query R
+SELECT CASE WHEN false THEN NULL::DECIMAL(10, 2) ELSE 1.2345::DECIMAL(5, 4) END
+----
+1.2345
+
+subtest end

pkg/sql/logictest/testdata/logic_test/cast

@@ -1446,7 +1446,7 @@ CREATE TABLE def_assn_cast (
   id INT4,
   a INT4 DEFAULT 1.0::FLOAT4,
   b VARCHAR DEFAULT 'true'::BOOL,
-  c NAME DEFAULT 'foo'::BPCHAR
+  c NAME DEFAULT 'foo'::CHAR
 )
 
 statement ok

pkg/sql/logictest/testdata/logic_test/decimal

@@ -468,7 +468,7 @@ NaN        NaN        NaN        NaN        NaN
 # TODO(drewk): There are a few differences vs postgres in the number of decimal
 # places and negative zeros.
 query RRRRR
-WITH v(id, x) AS (VALUES (1, '0'::numeric), (2, '1'::numeric), (3, '-1'::numeric), 
+WITH v(id, x) AS (VALUES (1, '0'::numeric), (2, '1'::numeric), (3, '-1'::numeric),
   (4, '4.2'::numeric), (5, 'inf'::numeric), (6, '-inf'::numeric), (7, 'nan'::numeric)
 )
 SELECT x1, x2,

pkg/sql/logictest/testdata/logic_test/drop_function

@@ -58,3 +58,33 @@ DROP FUNCTION f114677;
 
 statement error pgcode 42883 unknown function: f114677\(\)
 SHOW CREATE FUNCTION f114677;
+
+statement ok
+CREATE FUNCTION f_char(c CHAR) RETURNS INT LANGUAGE SQL AS 'SELECT 1'
+
+statement ok
+DROP FUNCTION f_char(BPCHAR)
+
+statement ok
+CREATE FUNCTION f_char(c CHAR(2)) RETURNS INT LANGUAGE SQL AS 'SELECT 1'
+
+statement ok
+DROP FUNCTION f_char(BPCHAR)
+
+statement ok
+CREATE FUNCTION f_char(c BPCHAR) RETURNS INT LANGUAGE SQL AS 'SELECT 1'
+
+statement ok
+DROP FUNCTION f_char(BPCHAR)
+
+statement ok
+CREATE FUNCTION f_char(c BPCHAR) RETURNS INT LANGUAGE SQL AS 'SELECT 1'
+
+statement ok
+DROP FUNCTION f_char(CHAR)
+
+statement ok
+CREATE FUNCTION f_char(c BPCHAR) RETURNS INT LANGUAGE SQL AS 'SELECT 1'
+
+statement ok
+DROP FUNCTION f_char(CHAR(2))