Auto merge of #18984 - dsandeephegde:master, r=jdm

 Initial steps of Mutation testing

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- Added one strategy of mutation which is replacing occurrences && to ||.
- Added test mapping framework for running mutation tests corresponding to a mutant.
- Added one test_mapping.json to map source file in a folder to WPT test.
- Added README mentioning about Mutation testing.
- Added CI script to invoke mutation test.
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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes #18529 (github issue number if applicable).
- [x] These changes do not require tests because it is a python script to run mutation test and does not change any behavior.

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