Add custom syntax highlighting config files

[RpxdYTX]

Is your feature request related to a problem? Please describe.
A lot of issues in this repo are related to "add support for language X". By adding a way to extend the editor syntax, both changes to existing syntax and support for new languages can be made easier.

Describe the solution you'd like
Add some kind of configuration files that would specify:

• The syntax name (to make it compatible with force syntax)
• The language extensions (which files have this syntax automatically)
• And the syntax specifications (which could be regex, like lite-xl)

Additional context
The only problem this would create is that syntax alterations are local to users, and a small margin would publish online to repos.