Add MySQL 8.0-compatible extended syntax for all REGEXP functions

Overview

MariaDB's regular expression functions are missing full MySQL 8.0 compatibility. While MariaDB has supported `REGEXP_INSTR()`, `REGEXP_REPLACE()`, and `REGEXP_SUBSTR()` since 10.0.5 (via the PCRE engine), their signatures are limited to the bare minimum arguments.
MySQL 8.0 introduced extended argument signatures, a `match_type` flag, the `REGEXP_LIKE()` function, and switched its regex engine from PCRE to ICU.

This ticket tracks the implementation of full MySQL 8.0-compatible syntax across all
regular expression functions.

`REGEXP_LIKE`: Missing entirely in MariaDB

MySQL 8.0 introduced `REGEXP_LIKE()` as a proper function form of the `REGEXP`/`RLIKE` operator.

REGEXP_LIKE(expr, pattern[, match_type])

`REGEXP_INSTR`: Missing optional arguments

-- MariaDB (current)

REGEXP_INSTR(subject, pattern)

-- MySQL 8.0 (target)

REGEXP_INSTR(expr, pattern[, pos[, occurrence[, return_option[, match_type]]]])

`REGEXP_REPLACE`: Missing optional arguments

-- MariaDB (current)

REGEXP_REPLACE(subject, pattern, replace)

-- MySQL 8.0 (target)

REGEXP_REPLACE(expr, pattern, repl[, pos[, occurrence[, match_type]]])

`REGEXP_SUBSTR`: Missing optional arguments

-- MariaDB (current)

REGEXP_SUBSTR(expr, pattern)

-- MySQL 8.0 (target)

REGEXP_SUBSTR(expr, pattern[, pos[, occurrence[, match_type]]])