Refactor rustc_on_unimplemented's filter parser

[mejrs]

Followup to #139091; I plan on moving most of this code into rustc_attr_parsing at some point, but want to land this separately first.

I have taken care to preserve the original behavior as much as I could:

• All but one of the new error variants are replacements for the ones originally emitted by the cfg parsing machinery; so these errors are not "new".
• the InvalidFlag variant is new, this PR turns this (from being ignored and silently doing nothing) into an error:

  #[rustc_on_unimplemented(on(something, message = "y"))]
  //~^ ERROR invalid boolean flag
  //~^^ NOTE expected one of `crate_local`, `direct` or `from_desugaring`, not `something`
  trait InvalidFlag {}

  This does not occur anywhere except in this test. I couldn't find a way that I liked to keep allowing this or to do nothing, erroring was the cleanest solution.
• There are a bunch of FIXME throughout this and the previous PR, I plan on addressing those in follow up prs..

Finally, this gets rid of the "longest" dependency in rustc:

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[rustbot]

These commits modify the Cargo.lock file. Unintentional changes to Cargo.lock can be introduced when switching branches and rebasing PRs.

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[mejrs]

r? compiler

[nnethercote]

Generally looks ok, a bunch of nitpicks below.

[nnethercote]

s/UnSupported/Unsupported/

[nnethercote]

Also, the variant name doesn't really match the message name: "unsupported" vs "unimplemented". It would be better if they were close to each other. Likewise for a couple of the other variants.

[mejrs]

I'm not sure what you mean. The unimplemented in the flt name references the name of the attribute, not what went wrong. But I have edited it to ...unsupported_literal_in_on

[mejrs]

Maybe consider having trait_selection_rou_* rather than trait_selection_rustc_on_unimplemented_*? I errored on the side of not abbreviating.