optimizations: better modeling and codegen for apply and svec calls (#59548)
- Use svec instead of tuple for arguments (better match for ABI which
will require boxes)
- Directly forward single svec argument, both runtime and codegen,
without copying.
- Optimize all consistant builtin functions of constant arguments, not
just ones with special tfuncs. Reducing code duplication and divergence.
- Codegen for `svec()` directly, so optimizer can see each store (and
doesn't have to build the whole thing on the stack first).
Written with help by Claude