SF: Fix mode setting for secondary displays

Desired modes were only propagated to HWC for the "active" display, i.e.
generally the primary display and specially the rear display when in the
folded state. In other words, mode setting did not happen for external
displays, and the rear display when driving both displays concurrently.

Store per-display state for whether a mode set is pending. Propagate the
desired mode for both internal and external displays as long as they are
powered on.

Fixes: 277776378
Fixes: 289182528
Bug: 255635711
Bug: 255635821
Test: The 60 Hz constraint applies to both displays in concurrent mode.
Test: ADB `set-user-preferred-display-mode` applies to external display.
Test: DisplayModeSwitchingTest#inner{Xor,And}OuterDisplay
Test: DisplayModeSwitchingTest#powerOffDuringModeSet
Change-Id: I9da3a0be07f9fbb08f11485aa6ab9400259a4e09
Merged-In: I9da3a0be07f9fbb08f11485aa6ab9400259a4e09