Perform API backwards compatibility check as part of support checkApi

Works around Doclava API check limitations in Snackbar and v17 classes.
Removes @removed code. Restores GuidedActionsStylelist API that was
removed without prior deprecation. Adds 26.0.0 to work around
non-binary-compatible changes that have been OK'ed by API Council.

Bug: 30434567
Test: ./gradlew checkApi
Change-Id: I58c8a869f4e620d2aca8765a73105c95c185c791
25 files changed