efactors the content_libraries.api to use LibraryCollectionLocator and LibraryContainerLocator keys, instead of passing separate LibraryUsageKeyV2 keys along with the collection/container locators.
Renames misleading uses of collection_usage_key to collection_locator, including in the content_libraries.api and content.search.api method names and parameters.
This change impacts Developers, but should not affect end users.
This refactoring seems reasonable to do without going through deprecation, given the minimal use of these APIs.
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