Switch to asfv1 parser

[aazuspan]

Major refactor to switch from a custom Lark parser to a parser based on asfv1. No point reinventing the wheel, since it's already a feature-complete parser for SPINAsm. We do need to hack some functionality onto the parser, including:

1. Track current column of the parser
2. Record when symbols are defined
3. Offset lines to zero-indexed
4. Record errors and warnings as LSP diagnostics
5. Prevent early exits when errors are encountered.

Those changes are all handled by the SPINAsmParser subclass of fv1parse.

This also includes a lot of incidental refactoring, additional documentation, more LSP features, LSP tests, etc.