Internalize @handlebars/parser

[NullVoxPopuli]

Internalizes: https://github.com/handlebars-lang/handlebars-parser

@glimmer/syntax currently has these dependencies:

    "@glimmer/interfaces": "workspace:*",
    "@glimmer/util": "workspace:*",
    "@glimmer/wire-format": "workspace:*",
    "@handlebars/parser": "~2.2.0",
    "simple-html-tokenizer": "^0.5.11"

and we don't actually use handlebars, so bringing in the parser is a good opportunity to make the parser do exactly what we need, and not a thing more (removing hacks to work around handlebars behaviors we don't support), etc.

Additionally, the handlebars parser has support for things we don't support.
So we'll need to reconcile that at some point.