wasapi: Improve stability of playback in Polling Shared mode with a l…

…ow host latency requsted (22 ms):

- Implement workaround for system timer coarse granularity causing underruns by using timeBeginPeriod/timeEndPeriod APIs inside the Event and Poll thread handlers.
- Update next sleep time of the Poll rendering loop dynamically depending on time taken for processing/rendering of audio data into the available host buffer to avoid underruns and fit processing time into periodic polling time slots.
- Add support for time slots logging in Poll mode if PA_WASAPI_LOG_TIME_SLOTS is defined. Fixed audible glitches by preloading the whole host buffer before stream is started.
- Fix audible glitches on stream start by preloading the whole host buffer before stream is started.