Lone `self` in a method body should resolve to the 'self parameter'

[mattheww]

In a method body, a path expression consisting only of the keyword self should resolve to the (binding of the) method's 'self parameter'.

I believe at the moment the FLS says this resolves to the containing module.

Example:

  struct MyType {
      x: (),
  }

  impl MyType {
      fn simple_method(self) {
          self.x;
      }
  }

Looking at the self.x FieldAccessExpression:

The part before the . is an UnqualifiedPathExpression whose single SimplePathSegment is the keyword self.

§14.9.4.2 "Path Expression Resolution" says (in fls_dc0yv4306p82) that we resolve the leftmost (and only) segment using general path resolution.

§14.9.4:12 (fls_ri50nc2dg7c4) says that a path segment which is the keyword self resolves to "the entity of the current module".

I've also filed rust-lang/reference#1427