Unit testing ButtonDropTarget

Originally there was a bug in a method (isTextClippedVertically) in ButtonDropTarget. While attempting to write a unit test it became necessary to refactor ButtonDropTarget and DeleteDropTarget to decouple them from their dependency on launcher in order to allow for a unit test to be written

The pattern we are introducing here is to decouple Launcher from a controller, in order to facilitate easier testing.
Instead of calling Launcher.getLauncher() we call the method through ActivityContext, which has a testing wrapper already defined. Here is a diagram that explains the old and new pattern

Design Pattern: https://screenshot.googleplex.com/7apiE2DaGDrFzy9.png

Test: isTextClippedVerticallyTest
Bug: b/274402490

Change-Id: I1f3003d0b62dddbceb6e492b15aa5d7352d3a293