Route FilterDirectory#copyFrom through createOutput (10x backport of #16530)

[tballison]

Backport to branch_10x of the non-breaking parts of #16530 (which follows up #16173).

Replaces #16538.

#16173 (backported to 10x in 148ee2f) changed FilterDirectory#copyFrom to delegate to the wrapped directory, which hid FilterDirectory subclasses that override createOutput for per-file bookkeeping (TrackingTmpOutputDirectoryWrapper, MockDirectoryWrapper, NRTCachingDirectory, DirectIODirectory, ByteWritesTrackingDirectoryWrapper).

Differences from #16530, since we can't break the API on 10x:

• Directory#copyFrom keeps its concrete default implementation (no abstract method, no copyThroughCreateOutput helper). FilterDirectory#copyFrom routes through super.copyFrom — i.e. through createOutput — instead of delegating, with javadoc noting that subclasses wanting an optimized copy (e.g. HardlinkCopyDirectoryWrapper) may override to delegate.
• The required implementations added on main (CompoundDirectory, FileSwitchDirectory, BaseMergePolicyTestCase) are unnecessary here and are omitted.
• TrackingTmpOutputDirectoryWrapper#copyFrom failure cleanup uses IOUtils.deleteFilesIgnoringExceptions since deleteFilesSuppressingExceptions (Catch and re-throw Throwable rather than using a success boolean #14633) is main-only.

Same as #16530:

• Fixes TrackingTmpOutputDirectoryWrapper#copyFrom failure cleanup to delete the temp file rather than the logical dest name.
• Ports the tests: TestFilterDirectory#testCopyFromRoutesThroughCreateOutput (replaces testCopyFromDelegates),
  TestTrackingTmpOutputDirectoryWrapper, TestByteWritesTrackingDirectoryWrapper#testCopyFromTracksBytes,
  TestDirectIODirectoryCopyFrom.

The CHANGES entry replaces the #16173 entry under 10.6.0 Bug Fixes since this reverts that behavior before it ships in a
release.

Note: Normal process would be to push this backport directly to branch_10x, I think. Since it reverts the behavior introduced by #16173, I'm opening a PR instead -- @msfroh, @iprithv, I'd appreciate your eyes on it before it goes in.

Thank you!