Add script to cleanup redundant BCD overrides

[queengooborg]

This PR adds a script that removes the compat_features overrides from web-features files when the overrides' data matches the data that comes from BCD tags.

[ddbeck]

I'd like to suggest renaming this. There are a few possible overrides in a .yml file: compat_features, compute_from, and complete status block and all of them involve BCD to some extent. And "clean" implies that overrides are necessarily "dirty" (some are not).

My naming ideas are:

• dedupe-compat-tags
• tidy-compat-features
• remove-tagged-compat-features

[ddbeck]

Ack, my top-of-review comment got lost:

Cool! I have some suggestions to make this safer to run and to improve maintainability, but I like the overall shape of this.

[jamesnw]

I pushed a fix to a bug in one of my earlier suggestions. Apart from the renaming question from @ddbeck, the other issue currently is with the output yaml formatting.

Adding a comment to the document adds a line of whitespace which the formatter removes. I think ideally we should run prettier on the output like we do in feature-init, or perhaps more crudely, update package.json to have-

"cleanup-bcd-overrides": "tsx scripts/cleanup-bcd-overrides.ts; npm run format" },