Auto merge of #29923 - mrobinson:test-scripts, r=jdm

Combine all script tests into `test-scripts`

Remove:
    - tidy self test support from `./mach test`
    - `./mach test-idl`

Adds a `./mach test-scripts` command that is responsible for running all
Python script tests. Run this during the CI to catch regressions in
changes to scripts. The WebIDL tests are still *very* slow and there are
from Gecko, so only run them when "-a" is passed meaning all tests.

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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] There are tests for these changes

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