Use font-lock-preprocessor-face for annotations

[charjr]

Changes

Separates Annotations from keywords so they can use a different face.

before	after

I picked the font-lock-preprocessor-face since GDScript TS Mode uses this already:

emacs-gdscript-mode/gdscript-ts-mode.el

Lines 161 to 164 in dde79a1

	:language 'gdscript
	:feature 'annotation
	'((annotation "@" @font-lock-preprocessor-face
	(identifier) @font-lock-preprocessor-face))

Side Note

The highlighting could be simplified to just take any string after an @ symbol, this would be more performant and less maintenance. But since the keywords exist and provide some additional completion, I just used them for now.

Simplified the regex to match Godot editor behaviour: Godot immediately highlights anything starting with @.

[charjr]

Just as further corroboration: The built-in php-ts-mode also uses font-lock-preprocessor-face for PHP's Attributes which are functionally similar to GDScript's Annotations.

   :language 'php
   :feature 'attribute
   '((((attribute (_) @attribute_name) @font-lock-preprocessor-face)

Where an attribute looks like this:

#[Attribute]
function foo ()

[charjr]

Did not mean to close it, sorry. I was squashing the commits (as the ones in the middle did not work on their own, so don't really provide a useful history).

@jcs090218 Sorry to be a bother but if you have the time, please may you review this?

If it's too big, I can reduce it to the change in gdscript-syntax.el. This would improve the highlighting.