ime: Fix a corner case in ConfirmCompositionText where commits get lost.

Here's a corner case in handling IME operations:

1) IME calls CommitText()
2) IMF receives CommitText and enqueues the operation as pending.
   This is because we may get more operations and they could be
   coalesced together.
3) IME calls FinishComposition()
4) IMF receives FinishComposition. FinishComposition is not enqueued.
   Instead, it is immediately executed, which resets the IMF state.
   We lose the pending commit as a result.

There's a long history around why certain things get queued and some
don't, but overall the pending commit/composition logic is very
convoluted.

To fix the root cause problem, we will either remove the pending
operation logic completely, or ensure all operations are queued
consistently.

For now, fix this problem for M100 by targeting this specific
scenario of calling ConfirmCompositionText when there's a pending
commit. Since the pending commit will destroy any composition,
ConfirmCompositionText will be a no-op in this case.

Fixed: 223075193
Change-Id: I7defbee25dffe46d856bd65b39cdef4c52dcd4fb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3530969
Auto-Submit: Darren Shen <shend@chromium.org>
Reviewed-by: Bao-Duy Tran <tranbaoduy@chromium.org>
Commit-Queue: Bao-Duy Tran <tranbaoduy@chromium.org>
Cr-Commit-Position: refs/heads/main@{#982113}