Add .c3i and .c3t to supported C3 extensions

[Alhadis]

Description

This pull-request fixes #8082 by adding support for the .c3i and .c3t file extensions to the C3 language, originally added by @rudywasfound in #7525.

/cc @0riginaln0

Usage

Search results for the c3t extension were a bit varied; most of them were unrelated JSON files (which this pull-request takes into consideration). The other unrelated files are a handful of GPL license files named things like LICENSE-GPL3_V1.c3t, but they don't have nearly enough usage on GitHub to qualify for addition (only ~24 results as of this writing). Filtering out both JSON and license texts gives us ~284 C3 files.

Extension	Language	Search query	Results
*.c3i	C3	path:**/?*.c3i	~233
*.c3t	C3	path:**/?*.c3t NOT /^\{|GNU GENERAL PUBLIC LICENSE/	~284
	JSON (Cocos2D‑X)	path:**/?*.c3t /^\{/	~5.2k

Checklist

• I am adding new extensions to a language.
  • The new extensions are used in hundreds of repositories:
    See above.
  • I have included real-world usage samples for each extension:
    • pq.c3i (MIT-licensed)
    • gamepad.c3i (MIT-licensed)
    • client_window.c3t (MIT-licensed)
    • ct_if_folding.c3t (MIT-licensed)
    • typefrom.c3t (MIT-licensed)
    • utils.c3i (MIT-licensed)
    • empty.c3t (GPL-3.0 licensed)
    • box.c3t (GPL-3.0 licensed)
  • I have included changes to the heuristics.
    Yes, to easily differentiate between a JSON file whose first non-blank character is {, and C3 statements that begin a line with a common (unquoted) keyword, which isn't legal JSON.

[rudywasfound]

LGTM