Apply the window decor transaction in sync with the View's draw

When the window decoration needs to #relayout from an
onTaskInfoChanged() call (usually due to resizing), the
SC.Transaction that set the new task crop was applied at the same
time as the View's layout was scheduled to draw, which meant that
when the View is slow to draw, the new task size is visible on screen
before the caption View is visible, which looks like a flicker.

This change merges the transaction with the buffer transaction from
the view root using #applyTransactionOnDraw, so that both are visible
at the same time on screen.

Bug: 270202228
Test: atest WindowDecorationTests
Test: manual - drag resize a freeform task, no flickering around the
edge of the caption.

Change-Id: Iccdc0acdd9935b0a89759704b2e4426802f2b44a