sql: fix JSON fetch value operator evaluation

This commit fixes incorrect evaluation of the JSON fetch value operator,
`->`. There were two bugs causing incorrect evaluation.

The first issue was a result of optimizer normalization rules that
produced unequivalent scalar expressions when converting `->` to `@>`.
The rules would convert expressions like `j -> '"a"' = 1` to
`j @> '{"a": 1}'`. This is invalid because `->` results in `NULL` when
the LHS does not contain the RHS key, but the resulting `@>` expression
is always either `true` or `false`, never `NULL`. These normalization
rules have been removed.

These two rules existed to provide inverted index-acceleration for
queries with `->`, because the optimizer can only index-accerlate `@>`
operators during exploration. As a result of their removal, queries with
`->` operators are no longer index-accelerated. This will be remedied in
a future commit.

The second issue was a bug in the vectorized overload of the `->`
operator. Previously, when the operator evaluated to `NULL` with two
non-`NULL` inputs, the resulting `NULL` would not be tracked by the
`Nulls` struct.

Fixes cockroachdb#49143

Release note (bug fix): Previously, the JSON fetch value operator, `->`,
would evaluate incorrectly in some cases. This has been fixed.

pkg/sql/colexec/execgen/cmd/execgen/overloads_bin.go

@@ -761,8 +761,11 @@ func executeBinOpOnDatums(prelude, targetElem, leftColdataExtDatum, rightDatumEl
 			if err != nil {
 				colexecerror.ExpectedError(err)
 			}
+			if _res == tree.DNull {
+				_outNulls.SetNull(%s)
+			}
 			%s
-		`, prelude, leftColdataExtDatum, rightDatumElem,
+		`, prelude, leftColdataExtDatum, rightDatumElem, idxVariable,
 		set(typeconv.DatumVecCanonicalTypeFamily, vecVariable, idxVariable, "_res"),
 	)
 }