Merge #5639

Merge #5639

5639: SSR: Allow `self` in patterns. r=jonas-schievink a=davidlattimore

It's now consistent with other variables in that if the pattern references self, only the `self` in scope where the rule is invoked will be accepted. Since `self` doesn't work the same as other paths, this is implemented by restricting the search to just the current function. Prior to this change (since path resolution was implemented), having self in a pattern would just result in no matches.

Co-authored-by: David Lattimore <dml@google.com>