Fix a bug in SpellCheckSpan update logic.

The the text is changed, we need to remove all affected SpellCheckSpan.
However, the previous check logic can not work correctly, and may
leave some out-of-date SpellCheckSpan, which causes problem when the
SpellChecker tries to apply suggestions on those spans later.

Also fixed the bug that the offset is not calculated correctly when we
validate spell checker suggestions.

Fix: 188107864
Change-Id: I8dc806d96b6a75255277d6de013305557835cb6d
Test: atest CtsInputMethodTestCases:SpellCheckerTest
Test: atest android.widget.cts.TextViewTest