Fix: EditText crash when insert emoji in insert mode

InsertModeTransformationMethod.TransformedText#getSpan returns wrong
spans when the given range is collapsed. This caused the EditText to
crash when insert mode and EmojiCompat are used together. This CL fixed
the above issue and also updated the tests.

Bug: 278153638
Test: atest InsertModeTransformationMethodTest
Change-Id: Ia036be0efc1cb358857ff827f0fba7d60fb58912