Tell user reasons when skipping traits ; Allow using arbitrary frb attribute as an indicator to include an item

[fzyzcjy]

Changes

Fixes #2103

Checklist

• An issue to be fixed by this PR is listed above.
• New tests are added to ensure new features are working. Please refer to this page to see how to add a test.
• ./frb_internal precommit --mode slow (or fast) is run (it internal runs code generator, does auto formatting, etc).
• If this PR adds/changes features, documentations (in the ./website folder) are updated.
• CI is passing. Please refer to this page to see how to solve a failed CI.

Remark for PR creator

• ./frb_internal --help shows utilities for development.
• If fzyzcjy does not reply for a few days, maybe he just did not see it, so please ping him.

[codecov]

Codecov Report

Attention: Patch coverage is 97.97980% with 6 lines in your changes missing coverage. Please review.

Project coverage is 99.12%. Comparing base (3ed6c2f) to head (8439c1b).

Files	Patch %	Lines
frb_codegen/src/library/codegen/ir/misc/skip.rs	89.65%	3 Missing ⚠️
...y/codegen/parser/mir/parser/function/real/owner.rs	90.00%	2 Missing ⚠️
...odegen/parser/mir/parser/function/real/argument.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           master    #2121    +/-   ##
========================================
  Coverage   99.11%   99.12%            
========================================
  Files         486      485     -1     
  Lines       19656    19793   +137     
========================================
+ Hits        19482    19619   +137     
  Misses        174      174            

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