Alert reviewers when most but not all keys with the same web-features tag are modified in a PR

This implies that html.elements.meta.name.responsive-embedded-sizing should be unflagged too.

I found this by checking the list of keys in web-features frame-sizing (source, dist) against the PR description, to see if I had the right keys there. It'd be… interesting to use web-features tags to do something like generate automatic review annotations like, "80% of the keys in web-features entry X changed, but not keys A, B, and C. Maybe you should review that?"

Originally posted by @ddbeck in https://github.com/mdn/browser-compat-data/pull/30429#discussion_r3988363146

And now to spell this out more explicitly. In that PR, the following keys were modified:

• api.Window.requestResize
• css.properties.frame-sizing
• css.properties.frame-sizing.auto
• css.properties.frame-sizing.content-block-size
• css.properties.frame-sizing.content-height
• css.properties.frame-sizing.content-inline-size
• css.properties.frame-sizing.content-width

All of those keys were known to the web-features entry frame-sizing. But the one other key attached to the same feature, html.elements.meta.name.responsive-embedded-sizing, was not modified.

It seems to me that it might be practical to automatically advise reviewers of data relationships like this. Even something rather general, along the lines of a "This PR modifies 88% of [link to feature entry on the explorer]" comment might be quite useful.

Start with the linked web-platform-dx/web-features frame-sizing.yml and frame-sizing.yml.dist entries, then investigate how pull requests in this repository are checked and annotated. Done means reviewers receive a useful warning when most, but not all, keys associated with a web-features entry are modified, including the omitted keys or feature link.