Add syntax highlighting for HAML.

[expeehaa]

Is your feature request related to a problem? Please describe.

HAML is a markup language commonly used as a replacement for ERB in Ruby on Rails projects. To make editing .haml files easier, I would like to have syntax highlighting.

Describe the solution you'd like

Implement HAML syntax highlighting in Lapce.

Describe alternatives you've considered

• Write a plugin that adds support.

Additional context

For the Atom editor, this is realised by a plugin: https://github.com/HarlemSquirrel/language-haml I have not looked into how easily this can be adapted, but I suppose it could at least be a starting point. I'ld be interested in implementing this myself.

[panekj]

There doesn't seem to be any tree-sitter grammar for haml and we track syntax highlighting support in #272