Backport php-cc-mode compatibility scaffolding

[zonuexe]

Summary

This is a compatibility backport from #812 rewrite/cc-free-php-mode that prepares master for the eventual CC Mode-free php-mode transition without changing the current default php-mode behavior.

• Add lisp/php-cc-mode.el as a forward-compatible alias for the current CC Mode based php-mode
  • php-cc-mode aliases php-mode
  • php-cc-mode-hook, php-cc-mode-lineup-cascaded-calls, and php-cc-mode-enable-backup-style-variables alias their current php-mode-* counterparts
• Add dormant lisp/php-style.el scaffolding for the variable-based style system
  • It is included in the package, but not yet wired into the active php-mode require graph
• Move shared php-mode-* customization variables from php-mode.el to php.el
  • Keeps current compatibility defaults on master (php-mode-coding-style remains pear, symfony2 remains available)
• Document the transitional php-cc-mode alias in CHANGELOG

Compatibility notes

This PR intentionally avoids switching the active php-mode implementation. The current CC Mode based php-mode remains the default for file associations and behavior.

The new php-cc-mode.el file is a transitional shim on master; when the rewrite branch is rebased on top of this PR, that shim is replaced by the real frozen php-cc-mode implementation.

Test plan

• make test
  • 92 tests run
  • 89 passed
  • 3 skipped
  • 0 unexpected

Additional rebase check performed locally:

• Rebasing rewrite/cc-free-php-mode onto this branch completed successfully after resolving expected scaffolding conflicts
• make test on the rebased rewrite branch: 99 tests, 96 passed, 3 skipped, 0 unexpected
• make test-cc on the rebased rewrite branch: 16 tests, 16 passed, 0 unexpected