Rename two part drag to freeform transitions

Rename the two part drag to desktop transitions so they are not confused
with TRANSIT_MOVE_TO_DESKTOP which is a one part transition that is
triggered by moving to desktop mode via the caption handle menu.

Bug: 291107449
Test: Build
Change-Id: I771d7560c8ac9464e5aa43ba86459a1f9e326c66