gh-110850: Add PyTime_TimeRaw() function (#118394)

gh-110850: Add PyTime_TimeRaw() function (#118394)

Add "Raw" variant of PyTime functions:

* PyTime_MonotonicRaw()
* PyTime_PerfCounterRaw()
* PyTime_TimeRaw()

Changes:

* Add documentation and tests. Tests release the GIL while calling
  raw clock functions.
* py_get_system_clock() and py_get_monotonic_clock() now check that
  the GIL is hold by the caller if raise_exc is non-zero.
* Reimplement "Unchecked" functions with raw clock functions.

Co-authored-by: Petr Viktorin <encukou@gmail.com>