Adds reuse of enum variant TypeId.

[esdrubal]

Description

We already do unification of expressions with type annotation when necessary, but these were not affecting enum variants because we used separate TypeIds for the expression and for the enum variant.

With this change the enum variant and the expressions will share the same TypeId, making unification to the expression to also affect the enum variant.

Fixes #5492
Fixes #5581

Probably helpful for #5559

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.

[github-actions]

Benchmark for d19994b

Click to view benchmark

Test	Base	PR	%
code_action	5.1±0.12ms	5.4±0.15ms	+5.88%
code_lens	287.8±3.38ns	308.5±18.08ns	+7.19%
compile	3.0±0.04s	3.0±0.03s	0.00%
completion	4.9±0.68ms	4.8±0.15ms	-2.04%
did_change_with_caching	2.9±0.04s	2.8±0.03s	-3.45%
document_symbol	985.9±39.20µs	983.3±26.21µs	-0.26%
format	75.0±3.51ms	74.6±1.66ms	-0.53%
goto_definition	356.9±7.06µs	358.9±5.24µs	+0.56%
highlight	8.8±0.13ms	9.1±0.12ms	+3.41%
hover	534.8±7.62µs	530.8±7.06µs	-0.75%
idents_at_position	121.7±0.32µs	121.6±1.16µs	-0.08%
inlay_hints	654.2±46.79µs	664.6±18.68µs	+1.59%
on_enter	497.5±11.24ns	483.7±12.34ns	-2.77%
parent_decl_at_position	3.6±0.03ms	3.7±0.05ms	+2.78%
prepare_rename	359.3±13.01µs	362.2±7.10µs	+0.81%
rename	9.1±0.19ms	9.4±0.17ms	+3.30%
semantic_tokens	1052.2±13.74µs	1028.2±10.33µs	-2.28%
token_at_position	355.7±2.38µs	360.0±2.38µs	+1.21%
tokens_at_position	3.7±0.66ms	3.7±0.03ms	0.00%
tokens_for_file	410.6±9.02µs	410.0±7.03µs	-0.15%
traverse	37.6±0.69ms	38.3±1.18ms	+1.86%

[ironcev]

This improves just one single case but makes worst many others. E.g,

let _: Enum<u8, _> = Enum<_, bool>::A(123);

There is a PR coming that fixes the mentioned PRs in a more detailed way. Currently we are unfortunately stepping on each others toes 😄

[esdrubal]

Converted this back to a Draft until the better PR that @ironcev is working on is available. Then we should be able to close this.

[ironcev]

Closed in #5643.