Add runtime check to avoid overwrite arg in Diag

[xizheyin]

I set up a debug_assert check for the arg method to make sure that args in Diag aren't easily overwritten, and I added the remove_arg() method, so that if you do need to overwrite an arg, then you can explicitly call remove_arg() to remove it first, then call arg() to overwrite it.

For the code before the #142015 change, it won't compile because it will report an error

arg `instance`already exists.

This PR also modifies all diagnostics that fail the check to pass the check. There are two cases of check failure:

1. Between the parent diagnostic and the subdiagnostic, or between the subdiagnostics have the same field between them. In this case, I renamed the conflicting fields.
2. For subdiagnostics stored in Vec, the rendering may iteratively write the same arg over and over again. In this case, I changed the auto-generation with derive(SubDiagnostic) to manually implementing SubDiagnostic and manually rendered it with eagerly_translate(), similar to fluent diagnostics can easily overwrite each others' fields/args #142031 (comment), and after rendering it I manually deleted useless arg with the newly added remove_arg method.

(Some formatting needs to be adjusted though)

r? @oli-obk

[rustbot]

Some changes occurred in match checking

cc @Nadrieril

HIR ty lowering was modified

cc @fmease

Some changes occurred in check-cfg diagnostics

cc @Urgau

Some changes occurred to the CTFE machinery

cc @RalfJung, @oli-obk, @lcnr

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

[oli-obk]

afaict the derive also eagerly translates, so we could just change the derive to also remove all those args again after the calls

[oli-obk]

These renames are unfortunate. We do want these to be fairly independently nameable. These are just there because we're not guaranteed the main diagnostic will have these values set, right? The fields are effectively redundant, so we could

• remove them (and rely on the main diagnostic to set them)
• change the assert to only prevent overwriting args if the value is different

Thoughts?

[xizheyin]

Yes, it needs to be adjusted.

For the fields that completely overlap with parent diagnostic, I deleted the fields, which will be better. I will rearrange these fields later.