_FoundationCollection is installed with an improper name

[compnerd]

We currently use the thick format install for _FoundationCollection but name the swiftdoc/swiftmodule $Arch.swift* rather than $Triple.swift*.

This is due to the install rules in the swift-collections repository.

[jmschonfeld]

While this is mainly about building swift-foundation, I think we'll need to fix these install rules in the swift-collections repo so I'm going to move this issue over to swift-collections to track the change there (edit: doesn't look like I can transfer from the swiftlang org to the apple org)