Revert "Revert "[ML1] Introduce RichInputMethodSubtype""

This reverts commit a63d0a8e.

This patch seems to be fine after all, but was submitted without its companion [ML1.1] patch causing a build breakage. Reverting the revert and submitting both at the same time seems like the right thing to do.

Change-Id: Ib8fefa40b74dcee0edb025a52dac9b35c82d49df