Add Answer Engine Indexing support for GDScript file types (.gd, .tscn, .tres).

[lizzieshinkicker]

Please describe the feature you want
Answer Engine Indexing support for GDScript file types (.gd, .tscn, .tres).

Additional context
We've been able to use Tabby with various locally hosted models (I'm partial to the Qwen-Coder series) that have been working great with Godot, a fast growing and multi-platform open-source engine used for game and application development. Tabby's inline integration with Godot's bespoke language, GDScript, has been working excellently (JetBrains as the IDE), but I've noticed we haven't been able to get Tabby's Answer Engine to index our repositories GDScript files (.gd, .tscn, .tres). This would provide context, improve suggestions, as well as be useful to ask Tabby high level questions about our repository.

[wsxiaoys]

Related:
Treesitter grammar: https://crates.io/crates/tree-sitter-gdscript
Example: #597

[faceCutWall]

@wsxiaoys I'd like to take this:)