Fix diff for compound when transforming actual [onto main]

[henrahmagix]

fixes #1317
fixes #1406
resolves #1319

I cherry-picked the commits from #1319 onto 3-12-maintenance, they applied without conflicts, then I ran the scripts called in the test CI action and they all passed. I pushed this to 3-12-maintenance...henrahmagix:fix-compound-redefined-actual-diff-on-3-12 just for good measure =)

I did the same on main, bundle installed fine, but I wasn't able to run any of the tests locally because I kept getting the following error:

$ script/run_build
============= Starting binstub check ===============
Checking required binstubs
============= Ending binstub check ===============
============= Starting specs ===============
/path/to/rspec-expectations/bin/rspec
Could not find compatible versions

Because every version of rspec-core depends on rspec-support ~> 3.12.0
  and every version of rspec-expectations depends on rspec-support = 3.13.0.pre,
  every version of rspec-core is incompatible with rspec-expectations >= 0.
So, because Gemfile depends on rspec-expectations >= 0
  and Gemfile depends on rspec-core >= 0,
  version solving has failed.

So I hope the tests pass similarly when run in CI because I can't confirm locally unfortunately ☺️

[pirj]

There’s something fishy going on with the 1.8.7 build and the implicit expectation detection.
Also activesupport in cukes

============= Starting cukes ===============
[105](https://github.com/rspec/rspec-expectations/actions/runs/7239633754/job/19722746571?pr=1440#step:8:106)
/home/runner/work/rspec-expectations/rspec-expectations/bin/cucumber
[106](https://github.com/rspec/rspec-expectations/actions/runs/7239633754/job/19722746571?pr=1440#step:8:107)
/home/runner/work/rspec-expectations/rspec-expectations/bundle/ruby/2.7.0/gems/activesupport-7.1.2/lib/active_support/core_ext/time/conversions.rb:62:in `<class:Time>': undefined method `deprecator' for ActiveSupport:Module (NoMethodError)

[JonRowe]

I think this is what is breaking the built, it seems antiquated [because it is] but 1.8.7 required:

thing.
to(

over:

thing
.to(

[pirj]

Thank you!
With this, the 4.0 pr is redundant.
Jon, do you mind merging thus and handling ci for diff-lcs separately?

[pirj]

Thank you for pushing this to completion, @henrahmagix !

[henrahmagix]

Thanks to you and Jon for fixing and finishing it! 🙌