Expose a few APIs in util collections.

These are either already exposed on other specialized collection variants or are exposed as public API on the androidx versions, or both.

With these APIs exposed, all of the unsupported app usage can be done through public API. As a result, all unsupported app usage is now locked to apps targeting API 28 or earlier.

Bug: 116877302
Test: none, no implementation change
Change-Id: I548d71319bffb0a6b529e380ea936df674dbf515