Add support for Interaction to Next Paint

[mmocny]

Adds support for Interaction to Next Paint (INP), an experimental Responsiveness metric.

This PR also:

• Added support for User Timings (performance.measure) for INP and FID. Added in options page.
  • (Could add timings for LCP and CLS as well, but these are less obvious)
• Removed support for "final" marking for metrics
  • This matches the feature being removed in web-vitals.js, and fixes FID which was broken in the extension.

TODO before landing:

• web-vitals.js needs updating to a version which supports INP
• Need an icon for INP (currently re-using the FID icon)

Optional Folllow-up work:

• User Timings for FID and INP overlap, which messes up the DevTools timings UI a bit. Could consider merging the labels.
• Add User Timings for LCP/CLS
• web-vitals.js may return more than one entry for INP. Could change the way we represent the User Timings to match accordingly.

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[mmocny]

(I also didn't update the version number in the manifest)