The great Input/GestureDetector/TimeVal spring cleanup (a.k.a., a saner main loop) (#7415)

* ReaderDictionary: Port delay computations to TimeVal
* ReaderHighlight: Port delay computations to TimeVal
* ReaderView: Port delay computations to TimeVal
* Android: Reset gesture detection state on APP_CMD_TERM_WINDOW.
  This prevents potentially being stuck in bogus gesture states when switching apps.
* GestureDetector:
  * Port delay computations to TimeVal
  * Fixed delay computations to handle time warps (large and negative deltas).
  * Simplified timed callback handling to invalidate timers much earlier, preventing accumulating useless timers that no longer have any chance of ever detecting a gesture.
  * Fixed state clearing to handle the actual effective slots, instead of hard-coding slot 0 & slot 1.
  * Simplified timed callback handling in general, and added support for a timerfd backend for better performance and accuracy.
  * The improved timed callback handling allows us to detect and honor (as much as possible) the three possible clock sources usable by Linux evdev events.
    The only case where synthetic timestamps are used (and that only to handle timed callbacks) is limited to non-timerfd platforms where input events use
    a clock source that is *NOT* MONOTONIC.
    AFAICT, that's pretty much... PocketBook, and that's it?
* Input:
  * Use the <linux/input.h> FFI module instead of re-declaring every constant
  * Fixed (verbose) debug logging of input events to actually translate said constants properly.
  * Completely reset gesture detection state on suspend. This should prevent bogus gesture detection on resume.
  * Refactored the waitEvent loop to make it easier to comprehend (hopefully) and much more efficient.
    Of specific note, it no longer does a crazy select spam every 100µs, instead computing and relying on sane timeouts,
    as afforded by switching the UI event/input loop to the MONOTONIC time base, and the refactored timed callbacks in GestureDetector.
* reMarkable: Stopped enforcing synthetic timestamps on input events, as it should no longer be necessary.
* TimeVal:
  * Refactored and simplified, especially as far as metamethods are concerned (based on <bsd/sys/time.h>).
  * Added a host of new methods to query the various POSIX clock sources, and made :now default to MONOTONIC.
  * Removed the debug guard in __sub, as time going backwards can be a perfectly normal occurrence.
  * New methods:
    * Clock sources: :realtime, :monotonic, :monotonic_coarse, :realtime_coarse, :boottime
    * Utility: :tonumber, :tousecs, :tomsecs, :fromnumber, :isPositive, :isZero
* UIManager:
  * Ported event loop & scheduling to TimeVal, and switched to the MONOTONIC time base.
    This ensures reliable and consistent scheduling, as time is ensured never to go backwards.
  * Added a :getTime() method, that returns a cached TimeVal:now(), updated at the top of every UI frame.
    It's used throughout the codebase to cadge a syscall in circumstances where we are guaranteed that a syscall would return a mostly identical value,
    because very few time has passed.
    The only code left that does live syscalls does it because it's actually necessary for accuracy,
    and the only code left that does that in a REALTIME time base is code that *actually* deals with calendar time (e.g., Statistics).
* DictQuickLookup: Port delay computations to TimeVal
* FootNoteWidget: Port delay computations to TimeVal
* HTMLBoxWidget: Port delay computations to TimeVal
* Notification: Port delay computations to TimeVal
* TextBoxWidget: Port delay computations to TimeVal
* AutoSuspend: Port to TimeVal
* AutoTurn:
  * Fix it so that settings are actually honored.
  * Port to TimeVal
* BackgroundRunner: Port to TimeVal
* Calibre: Port benchmarking code to TimeVal
* BookInfoManager: Removed unnecessary yield in the metadata extraction subprocess now that subprocesses get scheduled properly.

* All in all, these changes reduced the CPU cost of a single tap by a factor of ten (!), and got rid of an insane amount of weird poll/wakeup cycles that must have been hell on CPU schedulers and batteries..

frontend/apps/reader/modules/readerhighlight.lua

@@ -338,14 +338,14 @@ end
 -- to ensure current highlight has not already been cleared, and that we
 -- are not going to clear a new highlight
 function ReaderHighlight:getClearId()
-    self.clear_id = TimeVal.now() -- can act as a unique id
+    self.clear_id = UIManager:getTime() -- can act as a unique id
     return self.clear_id
 end
 
 function ReaderHighlight:clear(clear_id)
     if clear_id then -- should be provided by delayed call to clear()
         if clear_id ~= self.clear_id then
-            -- if clear_id is no more valid, highlight has already been
+            -- if clear_id is no longer valid, highlight has already been
             -- cleared since this clear_id was given
             return
         end
@@ -681,7 +681,7 @@ function ReaderHighlight:_resetHoldTimer(clear)
     if clear then
         self.hold_last_tv = nil
     else
-        self.hold_last_tv = TimeVal.now()
+        self.hold_last_tv = UIManager:getTime()
     end
 end
 
@@ -1124,9 +1124,8 @@ end
 function ReaderHighlight:onHoldRelease()
     local long_final_hold = false
     if self.hold_last_tv then
-        local hold_duration = TimeVal.now() - self.hold_last_tv
-        hold_duration = hold_duration.sec + hold_duration.usec/1000000
-        if hold_duration > 3.0 then
+        local hold_duration = UIManager:getTime() - self.hold_last_tv
+        if hold_duration > TimeVal:new{ sec = 3 } then
             -- We stayed 3 seconds before release without updating selection
             long_final_hold = true
         end