fix: Apply self type from generic trait constraint before instantiating identifiers

[vezenovm]

Description

Problem*

Resolves #5063

Summary*

After the turbofish PRs we want the ability to instantiate a variable from a generic trait. This was possible but it required a redundant type annotiation like such (assume H has been specified with a where clause):

let hasher: H = H::default()

Similarly to trait generics, we now add type bindings from a trait constraint if the trait impl is assumed to exist.
We now can just do:

let hasher = H::default()

Additional Context

Documentation*

Check one:

• No documentation needed.
• Documentation included in this PR.
• [] [For Experimental Features] Documentation to be submitted in a separate PR.

PR Checklist*

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.

[jfecher]

Does this fix #5065 and #4732 as well?

Edit: Confirmed that it does not fix #5065. I assume #4732 is unaffected as well then.

[jfecher]

LGTM