depName/lookupName -> depName/packageName

[rarkins]

Describe the proposed change(s).

Our approach to extracting and looking up dependencies might be easier to understand and align with external concepts if we:

• use packageName instead of lookupName (it's a package name we look up)
• default to extracting packageName and extract depName only if there's some sort of "alias" or "short name" for it, which 95% of the time doesn't happen

A challenge would be how to handle matchPackage... matching in packageRules. Most of the time depName===lookupName so it gets the same result, but there's times when we have a "short" name for depName which is currently being matched, and actually we have no way to match a package rule against lookupName. In future I would like depName to be mostly cosmetic but happy to add matchDepNames. The challenge is if we switch matchPackageNames to match against packageName then there may be some existing rules which no longer match.

Perhaps we could add matchDepNames, and then with matchPackageNames we first try to match against packageName and then fall back to depName and warn of a migration need is there's a match?

[rarkins]

Shall we do this along with #9940 in a major release at the end of the week? Maybe pause all non-essential PR merging Thursday evening and I can get it done Friday

[rarkins]

Closed by #14490