Fire composition events if composition has been started and completed in same edit session.

Some IMEs may start and complete composition within same edit session.
Therefore, we should still fire composition events at the moment where
we commit the text to blink.

This change also contains several refactors:
1. Refactor code in |CommitTextAndEndCompositionIfAny|.

2. Moves logic to set |new_text_inserted_| from |TSFTextStore::SetText|
to |TSFTextStore::InsertTextAtSelection| since IMEs may directly invoke
the latter method. We need to correctly set the |new_text_inserted_|
flag in order to push text states to blink.

3. |TSFTextStore::InsertTextAtSelection| may be called several times in
single edit session. Therefore, we need to aggregate all replacement
ranges into single |replace_text_range_|.

4. In |TSFTextStore::RequestLock|, we should also reset all caches such
as |new_text_inserted_| even when the function early returns.

5. In |TSFTextStore::RequestLock|, use the replace text end pos instead
of the cached |composition_start_| as the |new_composition_start|.

Bug: 1099125
Change-Id: Ibfa2ff284a183939596d9ea2a5e7105e8139b099
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2274245
Reviewed-by: Yohei Yukawa <yukawa@chromium.org>
Reviewed-by: Siye Liu <siliu@microsoft.com>
Reviewed-by: Anupam Snigdha <snianu@microsoft.com>
Commit-Queue: Siye Liu <siliu@microsoft.com>
Commit-Queue: Anupam Snigdha <snianu@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#788799}