SF: Restructure OutputLayer creation to remove displayId argument

The existing code was explicitly passing the displayId when creating an
OutputLayer, so that a HWC2::Layer could be created if applicable.

This patch makes a quick adjustment to the code so that the
compositionengine::Display instance overrides the base createOutputLayer
logic to create the HWC2::Layer, as it knows the displayId itself.

This is a minor cleanup prior to moving computeVisibleLayers to the
Output class.

Test: atest libsurfaceflinger_unittest libcompositionengine_test
Test: go/wm-smoke
Bug: 121291683
Change-Id: Ic7224ba445084b833b8c344436397372b2153d42