SF: Switch to internal display setup

Rather than call the public hotplug() functions, which may have
undesired effects, set the internal state directly for a display in the
middle of being connected.

[Test execution time not significantly reduced]

Test: libsurfaceflinger_unittest passes on Pixel XL
Bug: 74827900
Change-Id: I604ff7267e7ea3af94095ca05e288ef18e248ee5