Honor major-mode-remap-alist in php-mode-maybe

[zonuexe]

Interop fix for Emacs's built-in php-ts-mode (checked against Emacs 32.0.50).

The bug

php-ts-mode registers this on load:

;; To be able to toggle between an external package and core ts-mode:
(add-to-list 'treesit-major-mode-remap-alist '(php-mode . php-ts-mode))

and treesit-enabled-modes copies the entry into major-mode-remap-alist when the user opts in. So a user who installs this package and enables php-ts-mode is explicitly asking for php-ts-mode — Emacs core added that entry for our benefit.

They didn't get it for .php files. set-auto-mode applies the remapping to whatever auto-mode-alist names; entries pointing straight at php-mode honored it, but ".php"/".phtml" go through php-mode-maybe, which is not itself a remap target and called the derived mode directly. The result was inconsistent within the same configuration:

file	auto-mode-alist	resulting mode
a.stub	php-mode	remapped ✅
a.php	php-mode-maybe	not remapped ❌

The fix

Resolve the derived mode through major-mode-remap, so php-mode-maybe behaves as if auto-mode-alist had named the mode directly. major-mode-remap is Emacs 30+, hence the fboundp guard — on older Emacs the mode is used unchanged, exactly as before, so this is safe for the Emacs 27-supporting series.

A regression test is included. It uses a stub mode rather than php-ts-mode itself, so it does not depend on the PHP tree-sitter grammar being installed, and it is skipped where major-mode-remap does not exist. Verified that it fails before the fix and passes after.

What needed no change

php-base-mode is fine as-is. php-ts-mode declares php-mode an extra parent via derived-mode-add-parents, and our php-mode derives from php-base-mode, so once this package is loaded:

(derived-mode-all-parents 'php-ts-mode)
;; => (php-ts-mode php-mode php-base-mode prog-mode)

(derived-mode-p 'php-base-mode) already works in php-ts-mode buffers, and the php-base-mode docstring naming both modes is accurate. Note also that adding parents from our side would be actively harmful: derived-mode-add-parents replaces the extra-parents list, so it would clobber php-ts-mode's (php-mode) link.