Add CorrectionSpan and APIs to pass a secure CorrectionSpan to TextView

- CorrectionSpan is a span which has suggestions made by IME.
This has a function to change the current IME to other IME specified
in this span. For security reasons, only the current IME
is allowed to use this function through InputConnection.
(IME token is used for checking the validity of it.).

- CorrectionSpan stores following information:

flags, subtype Id, InputMethodInfo Id, suggests, locale, original string

Change-Id: Id3abc9ea4d11753cdc4f483a2bb3128f49ba198a