Refactor rustc_attr_data_structures documentation

[xizheyin]

I was reading through AttributeKind and realized that attributes like InlineAttr didn't appear in it, however, I found them in rustc_codegen_ssa and understood why (guessing).

There's almost no overall documentation for this crate, I've added the organized documentation at the top of lib.rs, and I've grouped the Attributes into two categories: AttributeKind that run all through the compiler, and the ones that are only used in codegen_ssa, such as InlineAttr, OptimizeAttr, InstructionSetAttr.

Also, I've added documentation for AttributeKind that further explains why attributes like InlineAttr don't appear in it, with examples for each variant.

r? @jdonszelmann

[rustbot]

Some changes occurred in compiler/rustc_attr_data_structures

cc @jdonszelmann

[jdonszelmann]

As per my previous comments, won't approve this PR for the time being despite it having some good changes.

[xizheyin]

I also remove the comments in variants of AttributeKind.
@rustbot ready

[jdonszelmann]

@rustbot author

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.

[xizheyin]

@rustbot ready

[jdonszelmann]

likely to conflict (minorly) with #138164, let's wait for that to merge (or preemptively rebase ontop of it). It's in the queue, judging by the state of which it'll take an hour or 8 for that to get through. Will look again tonight (european time)

[xizheyin]

Seems to not conflict with #138164, let me rebase it.

[jdonszelmann]

Once more, I won't merge this documentation here. Only a link to rustc_attr_parsing is all that's needed so we don't have to keep two sets of docs up to date.

[jdonszelmann]

@rustbot author

[xizheyin]

@rustbot ready

[xizheyin]

My understanding is that a link is added at the top of rustc_attr_data_structures, but the rest of the content is retained because the rest of the content points to the structures in rustc_attr_data_structures. Is that correct?

Or do I have to move all the documentation at the top of rustc_attr_data_structures/src/lib.rs into rustc_attr_parsing, and then just keep a link?

I may not have been too clear on whether it was the former or the latter. My understanding is the former, since the two crates have different responsibilities. And in my previous version, I mixed up part of the parsed documentation in rustc_attr_data_structures, so add a copy of the link.