Delegation: support coercion for target expression

[Bryanskiy]

(solves #118212 (comment))

The implementation consist of 2 parts. Firstly, method call is generated instead of fully qualified call in AST->HIR lowering if there were no generic arguments or Qpath were provided. These restrictions are imposed due to the loss of information after desugaring. For example in

trait Trait {
  fn foo(&self) {}
}

reuse <u8 as Trait>::foo;

We would like to generate such a code:

fn foo<u8: Trait>(x: &u8) {
  x.foo(x)
}

however, the signature is inherited during HIR analysis where u8 was discarded.

Then, we probe the single pre-resolved method.

P.S In the future, we would like to avoid restrictions on the callee path by Self autoref/autoderef in fully qualified calls, but at the moment it didn't work out.

r? @petrochenkov