Fix: IMEs don't receive onUpdateSelection when performs insertion mode

TextView implements insertion mode by applying a new
TransformationMethod. However, in TextView#setTransformation it will
call TextView#setText. As a result, TextView will call
InputMethodManager#invalidateInput and make the following
updateSelection invalid until the InputConnection was reestablished.
This CL fix the issue by avoiding calling setText in
setTransformationMethod and instead, update the text layout only.
This also avoid triggering TextWatchers on the TextView.

Bug: 300850862
Test: mannually enable the flag and test with atest TextViewTest
Change-Id: I2298e523e688d48bc86f055a371cc6688e20c77e