Basic tests for wrapper Collection factories in java.util.Collections

Basic test coverage for the wrapper Collections constructed by
the following static factory methods in java.util.Collections:

   checkedNavigableMap()
   checkedNavigableSet()
   checkedQueue()
   emptyNavigableMap()
   emptyNavigableSet()
   emptySortedMap()
   emptySortedSet()
   synchronizedNavigableMap()
   synchronizedNavigableSet()
   unmodifiableNavigableMap()
   unmodifiableNavigableSet()

These 11 methods under test are the only ones currently annotated
@hide in Collections.java; this CL provides sufficient test coverage
for those to be un-hidden in a follow-up CL.

Most (perhaps all) aspects covered by these tests are also covered
by guava-testlib-21.0 tests, but those are not yet available in
AOSP and would take 80min to run, whereas these new tests only take
a few seconds to run.

SpliteratorTester previously contained some overly strict assertions
that Spliterator.trySplit() != null. This CL relaxes this assumption
for non-empty spliterables but adds a separate assertSupportsTrySplit()
check in the places that previously exercised this strict test logic;
Where the old tests appeared to be testing the wrong collection (e.g.
in HashSetTest), this CL asserts the support for trySplit on what
appears to be the correct Collection, but does not otherwise fix the
existing test code.

Bug: 29935305
Test: CtsLibcoreTestCases
Change-Id: Ibeac242bb60df7b06a1c8c80dc744707f734d91c

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