Move features to feature2 that depend on features that use new feature syntax

[Turbo87]

Fixes #6135. Closes #6168.

Compared to #6168, this PR implements the fix in a way that features depending on newer syntax are recursively moved to features2 instead of moving them all unconditionally.

Probably best reviewed commit-by-commit :)

/cc @rust-lang/cargo

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.11%. Comparing base (2e5a4fe) to head (187b3c9).
Report is 7 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9551      +/-   ##
==========================================
+ Coverage   89.07%   89.11%   +0.04%     
==========================================
  Files         286      287       +1     
  Lines       28940    29053     +113     
==========================================
+ Hits        25779    25892     +113     
  Misses       3161     3161              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[weihanglo]

👋🏾! Is the migration of this done for all relevant crate index files.

[Turbo87]

@weihanglo yes and no. we only triggered a manual sync for clap. the other crates will update whenever they release a new version.