Add basic global statistics for input handler events

[Susko3]

Adds basic statistics to InputHandlers counting the total number of handled events.

This can aid when debugging input:

• check which handler the event came from
  • would be useful to confirm Fix Windows Ink events being handled as touch events #5309 (comment)
• quickly check if a single user input is being handled by multiple handlers (if multiple handlers' event counts increase from a single user action, it's probably a bug)
• if a need arises when debugging, the statistics can be made more specific (as was done in 3f4f735)

While most handlers have only basic Total events statistics, WindowsMouseHandler and AndroidTouchHandler have additional, specific statistics. I thought those were useful, so I included them.

Example of displayed global statistics:

(note that a handler is not shown until its statistic is increased, this helps reduce noise. eg. TouchHandler is not shown here)

The existing *Events under Input are not that useful for the purposes described above – those only count the number of events in a single input frame (at 1000 Hz) and are more suited to debugging lag from long event queues.