Add convenience wrappers for `type_dependent_defs`

[oli-obk]

Most uses of that method mostly directly unwrap or just want to know the DefId. So we could use several kind of convenience wrappers:

• fn opt_type_dependent_def(&self, id: HirId) -> Option<Def>
• fn type_dependent_def(&self, id: HirId) -> Def
• fn type_dependent_def_id(&self, id: HirId) -> DefId

[stepnivlk]

hey @oli-obk, happy to take this one if its still available

[oli-obk]

Wow that was fast! Yes of course! If you have any questions, don't hesitate to ask here or on discord/zulip.

[stepnivlk]

@oli-obk Hi again :).
So I started implementing proposed methods and updating calls to them over the codebase and I noticed one def_id extracting pattern when there's something like this:

if let Some(def) = self.tables.type_dependent_defs().get(expr.hir_id) {
  let def_id = def.def_id();
  // do something with `def_id`
} else {
  // do something else
}

It seems to me like we can introduce fourth method:
fn opt_type_dependent_def_id(&self, id: HirId) -> Option<DefId>

Allowing us to rewrite previous example as:

if let Some(def_id) = self.tables.opt_type_dependent_def_id(expr.hir_id) {
  // do something with `def_id`
} else {
  // do something else
}

Leading to little bit cleaner code. Let me know what you think.

[oli-obk]

Good idea!

[wesleywiser]

This can be closed now right?