[IL16] Improve getTextWithSuggestionSpan

Dynamically test for the presence of main dict suggestions. This
is much more potent and more accurate than the vaguely defined
boolean.
Also, resolve a TODO and avoid creating an object uselessly.

Not directly related, but helpful with:
Bug: 8636060

Change-Id: Ib1745f77ee6d9ec7cd8bbfa5a548652ec84ec902