Add glua support

[Be1zebub]

Adds gmod dialect support to improve compatibility with Garry's Mod extensions and setups.

Most Garry's Mod VS Code extensions requires associate .lua files with the glua language mode. Because of this, StyLua doesn't format these files out of the box unless you manually override the file association back to lua. Adding gmod as a recognized dialect fixes this workflow friction completely.

Note on syntax: This patch only adds compatibility for the standard Lua syntax used in GMod. Non-standard C-style operators (//, &&, ||, !) are intentionally excluded, as standard syntax is the widely accepted best practice in the GLua community anyway.