Implements a strategy to bring back picture in picture support for YouTube videos.
Picture in picture implementation is behind feature flag `kBravePictureInPictureForYouTubeVideos` enabled by default.
Test coverage has been extensively discussed and introduced to make sure:
- We don't have race conditions when injecting the JS script
- We don't inject the script multiple times on same page navigation
- We don't create side effects in case of unexpected changes, and/or serialzed flags don't match
- We inject/modify the serialized flags in case of partial match
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Co-authored-by: bridiver <34129+bridiver@users.noreply.github.com>
