Add test of various escape functions

As highlighted by the prior commit, writing correct escape functions is less
trivial than one might hope.

This test module tries to verify that different escaping functions behave
reasonably. It e.g. tests:

- Invalidly encoded input to an escape function leads to invalidly encoded
  output

- Trailing incomplete multi-byte characters are handled sensibly

- Escaped strings are parsed as single statement by psql's parser (which
  derives from the backend parser)

There are further tests that would be good to add. But even in the current
state it was rather useful for writing the fix in the prior commit.

Reviewed-by: Noah Misch <noah@leadboat.com>
Backpatch-through: 13
Security: CVE-2025-1094

src/tools/pgindent/typedefs.list

@@ -3709,6 +3709,9 @@ pam_handle_t
 parallel_worker_main_type
 parse_error_callback_arg
 partition_method_t
+pe_test_config
+pe_test_escape_func
+pe_test_vector
 pendingPosition
 pending_label
 pgParameterStatus