Cleaning up the P/Invoke signatures for QPF and QPC to avoid marshalling and pinning...

Cleaning up the P/Invoke signatures for QPF and QPC to avoid marshalling and pinning (#36071)

* Cleaning up the P/Invoke signatures for QPF and QPC to avoid marshalling and pinning

* Responding to PR feedback.

* Dropping support for low resolution stopwatch

* Removing BestFitMapping=false

* Removing unneeded unsafe declarations

* Addressing more PR feedback

* Fixing the pal_time header file

* Fixing the Unix P/Invoke signatures for GetTimestamp and GetTimestampResolution to return ulong.

* Fixing GetTimestampResolution to scale the result for HAVE_CLOCK_MONOTONIC

Signed-off-by: dotnet-bot <dotnet-bot@microsoft.com>