Preserve documentation and hook string semantics

[sirreal]

Fixes #254.

What changed

• Stop applying namespace cleanup to every exported string.
• Normalize AST names at expression and metadata boundaries, preserving established JSON for defaults, constants, references, and call metadata.
• Export literal hook names with PHP string semantics.

Why

The PHP-Parser 5 compatibility cleanup treated documentation and hook literals as identifiers. It removed meaningful backslashes. Simply deleting that cleanup also caused broad JSON churn such as false becoming \false.

Keep syntax normalization where it belongs. Leave text alone.

Testing

• npm run test:phpunit — 28 tests, 158 assertions; 11 pre-existing PHPUnit deprecation warnings.
• php tests/prep-diff-test.php
• Full wp-includes export: expected documentation escapes remain; no stray global prefixes in defaults, constant values, references, or call-class metadata.