Allow renaming between self and first param with owned parameters

[Veykril]

This fixes renaming owned SelfParams turning the parameter into a reference, as in, for a type Foo, fn foo(self) {} became fn foo(renamed_name: &Foo) {} prior to this.

Similarly for the other way around, we now support renaming non-ref parameters to self. Additionally we do more checks now than before. We check:

• that the function has an impl block
• that we are renaming the first parameter(prior we ignored which parameter was renamed and always picked the first nevertheless)
• that the parameter's type aligns with the impl block(minus one level of reference abstraction to account for &self/&mut self)

[matklad]

bors r+

[bors]

Build succeeded:

• TypeScript (windows-latest)
• Rust (ubuntu-latest)
• Rust (windows-latest)
• Rust (macos-latest)
• TypeScript (ubuntu-latest)