Merge lp://qastaging/~andreas-pokorny/mir/use-monotonic-clock-for-input into lp://qastaging/mir

Switch to monotonic clock for everything input related

sytemTime from android-input is used by client and server within the input receiver to calculate an assumed frame time, and to attach timestamps to input events. The evdev platform now ensures with EVIOCSCLOCKID(CLOCK_MONOTONIC) that for every device opened through libinput CLOCK_MONOTONIC is used. Note that EventHub.cpp does the same.
KeyRepeatDispatcher used to emit timer events from system_clock which uses CLOCK_REALTIME. Similar reports and fake event devices required adaptation too.

Before this change CLOCK_REALTIME was used because the default build configuration of android-input refrained from using any other clock (c.f. HAVE_POSIX_CLOCKS). Hence the input event timestamps were replaced by CLOCK_REALTIME timestamps. And everything else had to follow that setup.

As opposed to the previous attempt, this MP does not introduce the idea of a Clock passed to platforms. Instead it relies on the underlying system to come up with good timestamps. Especially for evdev events the timestamps from the device are more accurate than the ones generated when the system compositor gets to interpret the results from libinput.

So in the end this MP just changes the already spread time stamp related bits to use the monotonic clock.