More simplifications based on recent review comments:

[copybara-service]

More simplifications based on recent review comments:

• FunctionalEquivalence: Migrate from c.g.common.base.Objects.hashCode to j.u.Objects.hash.
  • (We can't static import it because Equivalance declares its own hash method.)
• Predicate: Migrate Javadoc from c.g.common.base.Object.equal to j.u.Objects.equals.
• Predicates: Tweak generics, at which point we can eliminate our local asList method and some explicit type arguments
• various files: Rename+move Iterators.checkNonnegative to CollectPreconditions.checkNonnegativeIndex to clarify how it differs from CollectPreconditions.checkNonnegative—namely, by throwing IndexOutOfBoundsException instead of IllegalArgumentException.
  • Thanks to Gemini for catching my mistake of trying to use the existing CollectPreconditions.checkNonnegative!
  • This change also changes the error message slightly. I could have left it alone, but I figured it might as well match the format we're using for the similar methods in CollectPreconditions.
  • I had thought that perhaps we could use Preconditions.checkPositionIndex, but (a) that requires a size (which appears in the exception message, so we shouldn't just pass MAX_VALUE) and (b) that throws IllegalArgumentException, too, wait, seriously? What were we thinking in cl/9392102 back in 2008?
    • I'll bet that many (most?) of our usages of checkPositionIndex are wrong. Certainly that's true of the first one that I looked at.
• various files: Remove suppressions of StaticImportPreferred for min/max methods that are in scope. The suppressions are no longer necessary as of cl/897308244, which avoids trying to static import when a method of the same name is already in scope.
  • Or actually, they're not necessary as of the earlier cl/811482021, which removed those suggestions from StaticImportPreferred entirely.
  • I kept the suppression in Booleans. That one exists because Comparator.min does not exist under all versions, so the fix of cl/897308244 is presumably not always sufficient.
    • Again, that's technically not necessary because StaticImportPreferred doesn't make the suggestion at all anymore (for exactly this reason). I suppose that I could tweak it to suggest min/max again as long as we're not inside a Comparator, but StaticImportPreferred is controversial in general, so I don't think that's necessarily worthwhile.
• various files: Static import min/max where we can (by locally undoing the exclusion for those methods :)).
• various files in the backport: Static import CollectPreconditions methods in a few more cases.

RELNOTES=n/a