sql: fix internal error when trying to parse strings as arrays

The parse-constant-as-type code was allowing a desired type of `Array[Any]`, and
we can't parse elements as `Any`. This resulted in an internal error, rather
than a normal query error.

Fixes cockroachdb#52134.

Release note (bug fix): Fixed an internal error involving string literals used
as arrays.

pkg/sql/logictest/testdata/logic_test/array

@@ -240,6 +240,10 @@ SELECT ARRAY['a', 'b', 'c'][0]
 ----
 NULL
 
+# Regression test for #52134: make sure this is not an internal error.
+query error cannot subscript type string because it is not an array
+SELECT '{a,b,c}'[0]
+
 query T
 SELECT (ARRAY['a', 'b', 'c'])[2]
 ----

pkg/sql/sem/tree/constant.go

@@ -59,7 +59,7 @@ func isConstant(expr Expr) bool {
 
 func typeCheckConstant(c Constant, ctx *SemaContext, desired *types.T) (ret TypedExpr, err error) {
 	avail := c.AvailableTypes()
-	if desired.Family() != types.AnyFamily {
+	if !desired.IsAmbiguous() {
 		for _, typ := range avail {
 			if desired.Equivalent(typ) {
 				return c.ResolveAsType(ctx, desired)