Improve guava-android Animal Sniffer compatibility testing for Java 8+ APIs

[cpovirk]

As of 33.2.0 (and even slightly earlier for package-private and guava-testlib APIs), we have APIs in our Android flavor that require library desugaring. For them, we disable Animal Sniffer. We could do better by having multiple Animal Sniffer runs:

• the current one, which flags anything that requires a newer version than Lollipop
• another one that flags anything that requires a newer version than Nougat (the version that we might work with without library desugaring)
• another one that flags anything that requires more than Lollipop + library desugaring
• another one that flags anything that requires more than Java 8

Then we'd want to use 2 slightly different sets of annotations to disable Animal Sniffer:

• one set that disables all those checks (in case we want to conditionally use an API that might not be available)
• one that disables only the first check

This is not a great description of what I'm going for, but I wanted to get down some rough notes after already touching on this in the linked TODO and in the release notes.