Add API to differentiate grammar suggestions.

The following attributes are added for grammar suggestions.
- SuggestionSpan#FLAG_GRAMMAR_ERROR
- SuggestionsInfo#RESULT_ATTR_LOOKS_LIKE_GRAMMAR_ERROR

Bug: 166304720
Test: atest CtsInputMethodTestCases:SpellCheckerTest
Change-Id: I0e5da3125d28bb881e513d0d69e0a2d336a9f286