[JuliaLowering] Implement static parameter capture (#62374)
Static parameter capture is (as far as I know) the last non-trivial,
non-performance piece of JuliaLowering that doesn't match flisp
yet. I kind of understand why it was left unimplemented.
This PR:
- Don't do the flisp renaming-sparams-early step, since it just makes
the hard parts of this harder.
- Change the `method` form out of desugaring to be `(method argtype_svec
lambda)` and fully construct the svec after its contents are known
- Change the `method_defs` form to be `(method_defs id typevar_list
body)`, because typevar_list should always precede lifted stuff in closure
conversion, and because special resolution needs to happen when each
`(typevar a b)` gets resolved (resolve b first, then declare a).
- This is kind of a hack, but I didn't want deeply-nested scope blocks.
These were previously declared as locals, which had the wrong scope
resolution (they could all see each other), and this was a pkgeval
problem.
- Add new binding kind `:typevar`. This behaves like a local up until
before linearization, and more like an ssavalue after that.
- In scope resolution, we collect the mapping from static parameter to
typevar, so that inner method signatures may resolve successfully (and
even re-use the original typevar)
This change also implements "underscore sparams are readable" #60626 and
ports #57928 (sparam capture in opaque closure is more like capture of
locals). It does not fix the pkgeval bug @topolarity reported to me with same-
named functions that require different closure types.
I've also added a cleaned-up Claude fix for typevars that depend on each
other in their bounds. Not sure if it's the best way of doing this. There's
an easy way out if this approach doesn't work (flisp just creates typevars
`<:Any` in closures).
