Ensure to inject events outside of the insets region for right margin

The display's x-coordinates for input are in the range:
  [0, displayWidth).

Injecting input at the point (displayWidth, 0) is technically outside
of the display. After accounting for insets, the x-coordinate range for
the display is:

  [leftInset, displayWidth - rightInset).

An input event injected at x = (displayWidth - rightInset) would be
outside of this range, and would be within the right insets region.

To account for this, use a one pixel buffer when calculating the
right gesture start margin.

A similar one pixel buffer is already used for the bottom margin
calculation.


Test: atest NexusLauncherTests:
com.android.quickstep.TaplTestsQuickstep
Bug: 208849306

Change-Id: I9d5a6429cd55fdfcbf2c849e27e3d3a0a7faaa47