Text selection: Fix moving by character when should move by word

The code to restrict handles from crossing did not respect moving by
word or by character. This CL checks the offset to see if it's crossing,
and if it is, it restricts it to the line of the other handle and proceeds
with determining the "actual" offset based on the activated
mode by word / by char).

There is also still a check to ensure that one character is selected
after the mode as adjusted the offset.

Bug: 21114827
Change-Id: Idac699ef2eb5d313e77d44b5064c03ff84e0fb88