meta: Extract revset parser as a separate crate

[pksunkara]

I am working on a VSCode plugin and extracting the revset parser is needed for it. So, I submitted this PR. There were a few things I couldn't decide:

The following don't probably belong in jj_revset_parser crate, but it needs them:

• content_hash.rs (and thus the proc_macro was changed)
• ref_name.rs
• fmt.rs (extracted from lib/src/revset.rs)

Checklist

If applicable:

• I have updated CHANGELOG.md
• I have updated the documentation (README.md, docs/, demos/)
• I have updated the config schema (cli/src/config-schema.json)
• I have added/updated tests to cover my changes
• I fully understand the code that I am submitting (what it does,
  how it works, how it's organized), including any code drafted by an LLM.
• For any prose generated by an LLM, I have proof-read and copy-edited with
  an eye towards deleting anything that is irrelevant, clarifying anything
  that is confusing, and adding details that are relevant. This includes,
  for example, commit descriptions, PR descriptions, and code comments.

[martinvonz]

I am working on a VSCode plugin and extracting the revset parser is needed for it.

Why can you not depend on jj-cli?

[pksunkara]

I am trying to compile the revset parser to wasm, which I am unable to do for jj_lib.

$ cargo check -p jj-lib --target wasm32-unknown-unknown

[yuja]

You could use the tree-sitter parser. It should be able to handle text with syntax errors better (if that matters).

https://github.com/bryceberger/tree-sitter-jjrevset

[PhilipMetzger]

This also is conflicting with my jj-core crate work FYI.

[PhilipMetzger]

I am trying to compile the revset parser to wasm, which I am unable to do for jj_lib.

$ cargo check -p jj-lib --target wasm32-unknown-unknown

yes, building the library with wasm-unknown-unknown is a big headache, which also requires many downstream adjustments (see this Discord thread), I hope jj-core crate will also make parts of that easier.

[pksunkara]

@PhilipMetzger If everything in this PR can be moved to jj-core crate, can we merge this (after I rename the crate)? We can incrementally add things to jj-core instead of waiting for a big PR.

[yuja]

I'm not sure if the whole revset modules will be moved to jj-core. Maybe the revset parser and non-essential types will be placed between jj-core and the new jj-lib?

#6284 (comment)

[pksunkara]

#9766 moved all of these into core.