Generate treesitter grammar

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

Currently, more and more tooling and editors are relying on [treesitter](https://tree-sitter.github.io/tree-sitter/) for navigation, parsing and semantic highlighting (e.g. in-browser VScode, nvim, github,), we should provide TS grammar for F#.

**Describe the solution you'd like**

TS grammar should be (if possible) generated from our fsl/fsy and hosted in the repo.

**Links**
Treesitter docs: https://tree-sitter.github.io/tree-sitter/
Existing grammars, incl. some ws-sensitive:
OCaml: https://github.com/tree-sitter/tree-sitter-ocaml
Python: https://github.com/tree-sitter/tree-sitter-python
Yaml: https://github.com/ikatyang/tree-sitter-yaml
Haskell: https://github.com/tree-sitter/tree-sitter-haskell