Add support for semantic / tree-sitter

It would be really cool if AST Explorer was able to support 'Semantic' and/or 'Tree-Sitter':

- https://github.com/github/semantic
- > Parsing, analyzing, and comparing source code across many languages
- https://github.com/tree-sitter/tree-sitter
- > An incremental parsing system for programming tools
- https://github.com/tree-sitter/tree-sitter/blob/master/lib/binding_web/
- > WebAssembly bindings to the Tree-sitter parsing library.
- https://github.com/tree-sitter/tree-sitter/tree/master/cli
- > The Tree-sitter CLI allows you to develop, test, and use Tree-sitter grammars from the command line.
- https://github.com/tree-sitter/node-tree-sitter
- > Node.js bindings for tree-sitter

---

> Tree sitter's WASM distribution seems to be able to create an AST in browser:
>
> [npmjs.com/package/web-tree-sitter](https://www.npmjs.com/package/web-tree-sitter)
>
> _Originally posted by @privatenumber in https://github.com/fkling/astexplorer/issues/622#issue-1087317072_

See also:

- https://github.com/tree-sitter/tree-sitter/tree/master/lib/binding_web