Implements aliases support in DCA.

[esdrubal]

Description

Adds support for aliases in DCA.

Fixes #4328 where a DCA warning was emmited while using struct method defined in an impl self.

Closes #4283
Closes #4328

Checklist

• I have linked to any relevant issues.
• I have commented my code, particularly in hard-to-understand areas.
• I have updated the documentation where relevant (API docs, the reference, and the Sway book).
• I have added tests that prove my fix is effective or that my feature works.
• I have added (or requested a maintainer to add) the necessary Breaking* or New Feature labels where relevant.
• I have done my best to ensure that my PR adheres to the Fuel Labs Code Review Standards.
• I have requested a review from the relevant team or maintainers.

[mohammadfawaz]

I did not understand the purpose of call_path_decl. What does it contain exactly? And why do we only need it in certain situations? (example: only for enums but not structs)

[esdrubal]

I did not understand the purpose of call_path_decl. What does it contain exactly? And why do we only need it in certain situations? (example: only for enums but not structs)

call_path_decl is needed for the DCA to be able to retrieve a type alias. For instance in the example below we have EnumScrutinee which contains enum_ref: DeclRefEnum already resolved to an enum, it is impossible to infer if we used a type alias from that. So I added call_path_decl which may be an alias or an enum decl.

sway/sway-core/src/language/ty/expression/scrutinee.rs

Lines 27 to 31 in 9b80160

	EnumScrutinee {
	enum_ref: DeclRefEnum,
	variant: Box<TyEnumVariant>,
	/// Should contain a TyDecl to either an enum or a type alias.
	call_path_decl: ty::TyDecl,

Structs should also have it, I probably forgot to add tests cases for structs, I will check that.

[esdrubal]

Fixed merging conflicts. And added one more test case and a fix for it.

The reason we have call_path_decl in EnumScrutinee and not in StructScrutinee is because we build an UnsafeDowncast from EnumScrutinee. The DCA uses UnsafeDowncast to connect match statements to the enum variants. In case we use an alias in the enum we need call_path_decl in UnsafeDowncast to contain the type alias decl.