Unifies the finger-to-cursor distance between drag cursor and drag handle.

This cl also fixes the way to simulate the touch events in EditorCursorDragTest, with correct raw X/Y.

Bug: 150534899
Test: manual & automated tests
  atest FrameworksCoreTests:EditorCursorDragTest
  atest FrameworksCoreTests:TextViewActivityTest

Change-Id: I0e9ef73082534ab98ddeddee0218374ed6d556a2