Merge data.extended.json into data.json

[rviscomi]

Progress on #3060

• generate by_compat_key data as part of the main index script for data.json
• continue making data.extended.json available in the GitHub release artifacts for backwards compatibility
• update docs and workflows

[ddbeck]

Overall, I'd very much like to get the extended data into the web-features package and I'm supportive. That said, I've got two main suggestions here (more detail in line comments):

• I'd prefer to change the way we generate data.json so that it's equivalent to data.extended.json. I think the one and only place we should have a data.extended.json is in the GitHub release artifacts (so that anyone depending on that URL still gets the data, at least until our next breaking release).
• I'd prefer to introduce utility functions separately. I think there's more discussion to have on that front and I don't want it to block providing the full data set.

[ddbeck]

Oh, one more thing: I pretty sure by_compat_key ought to be a required key in the schema, when we land this.

web-features/schemas/data.schema.json

Lines 300 to 308 in 5e81ac2

	"by_compat_key": {
	"description": "Statuses for each key in the feature's compat_features list, if applicable. Not available to the npm release of web-features.",
	"type": "object",
	"additionalProperties": {
	"$ref": "#/definitions/Status"
	}
	}
	},
	"required": ["baseline", "support"],

[rviscomi]

Oh, one more thing: I pretty sure by_compat_key ought to be a required key in the schema, when we land this.

I tried this, but by_compat_key depends on compat_features, which is optional. If we really want it to be required, should compat_features be required too? We could initialize both to empty objects and arrays respectively, but I'm not sure that adds much value.