CE: Output::setDisplaySize should change only bounds

In ag/12638299 we made setDisplaySize to change both bounds and
content. This breaks the case when the client has already changed the
content using setProjection. This CL reverts the previous behaviour
and adds a test for the broken scenario.

Bug: 169877274
Test: atest libsurfaceflinger_unittest libcompositionengine_test
Change-Id: Ia7df2074edb9e08fc66382bcf79df36d7d41cbd3