Link to corresponding sections for enum variants in rustdoc

[RDambrosio016]

resolves #74849 (for structs rustdoc shows fields omitted, so i am not sure if that should be removed and replaced for this)

This makes the text for each variant in an enum declaration a link to their corresponding section. As for the color that must be decided, i am by no means a design expert, i chose the color used for statics since it looked nice and not overbearing. But if you have an idea for a better color feel free to comment!

@Aaron1011 For structs do you mean rustdoc should render fields as well with clickable links for the fields?

Example of the output on dark theme

[rust-highfive]

Some changes occurred in HTML/CSS/JS.

cc @GuillaumeGomez

Some changes occurred in HTML/CSS themes.

cc @GuillaumeGomez

A change occurred in the Ayu theme.

cc @Cldfire

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @GuillaumeGomez (or someone else) soon.

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[Cldfire]

As far as the colors go, I played around with the blues a bit and came up with:

• Light theme: #2f71b3

• Dark theme: #8eb4db

• Ayu theme: #98c1ee

They all have good contrast for their respective backgrounds and fit in well with the surrounding colors.

Something else I noticed was that in the light and dark themes, we went from:

to, after this PR:

(layout: is colored now.) We should color the enum variants down there instead since that's the color that corresponds to the new links (or maybe we could leave them uncolored?).

[GuillaumeGomez]

I'm not a big fan of adding link in code blocks nor adding extra colors to the fields description (I don't mind adding colors in the type code block though).

[Aaron1011]

resolves #74849 (for structs rustdoc shows fields omitted, so i am not sure if that should be removed and replaced for this)

@RDambrosio016: I think that's only for private fields/structs. For example, rustc_infer::traits::Obligation shows all of the fields. I think it would be useful to generate links for structs as well.

@GuillaumeGomez: I think links in code blocks are very useful, especially for larger enums. For example, having links on rustc_hir::ExprKind would make it much easier to read the description for any particular variant.

[GuillaumeGomez]

You already have all the links in the sidebar.

[Aaron1011]

@GuillaumeGomez: Personally, I find it easier to read through the code block enum declaration, rather than looking at the sidebar. Types used in codeblocks already have links - is there any harm in adding more?

[GuillaumeGomez]

Which types in codeblocks already have links?

Also, I said I don't like it but if people are in favor, then we'll merge it, don't worry. ;)

[Aaron1011]

@GuillaumeGomez: Any type used in a codeblock (other than a plain generic parameter T) has a link: see the pages I listed in #75178 (comment) for examples

[GuillaumeGomez]

This is a good argument.

[GuillaumeGomez]

Ok, I've been thinking about it for a while, and here's my conclusion: this is a good idea. However, we should also do it for all types with fields (as long as we provide a section for the fields). What do you think?

Otherwise, great work here!

[RDambrosio016]

It has been decided this feature should be expanded to be more expansive, and it should be incrementally implemented, therefore i will be closing this PR and opening a tracking issue. Then incrementally opening PRs to add this.