Add Rust parser bridge helpers

[adamziel]

Summary

When a native MySQL parser extension declares WP_MySQL_Native_Parser, load a small bridge file that exposes WP_Parser_Grammar internals to the extension. The native parser needs the grammar's terminal table, rules, and lookahead map, but those live on a PHP object — the bridge function hands them out as a plain array the extension can consume.

The bridge file lives under mysql/native/ since it's only required when a native parser is in use.

Testing

• php -l on changed files
• phpcs clean