Implement higher precision clock than time_ns

[lzchen]

Followup to #1594

Currently, we use time_ns() to denote current time in ns -> like here

opentelemetry-python/opentelemetry-sdk/src/opentelemetry/sdk/_events/__init__.py

Line 54 in 3ae1138

timestamp=event.timestamp or time_ns(),

According to Pep0564, the precision varies based off of OS (with testing the average step is that of ~1ms in Windows). Java has implemented an AnchoredClock class which provides much more precise readings of ns (100~ns). We might want to do something similar in our SDKs.

Relevant issue: open-telemetry/semantic-conventions#1621 (comment)

[lmolkova]

Also open-telemetry/semantic-conventions#1701