Add in_trio_run and in_trio_task

[A5rocks]

Fixes #2757

See the documentation and tests for the cases in which these two differ. Feel free to ask me to add more scenarios.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00000%. Comparing base (d7cb2fc) to head (ce97b8a).
Report is 11 commits behind head on main.

Additional details and impacted files

@@               Coverage Diff               @@
##                 main        #3195   +/-   ##
===============================================
  Coverage   100.00000%   100.00000%           
===============================================
  Files             124          124           
  Lines           18733        18792   +59     
  Branches         1265         1268    +3     
===============================================
+ Hits            18733        18792   +59     

Files with missing lines	Coverage Δ
src/trio/_core/__init__.py	100.00000% <ø> (ø)
src/trio/_core/_run.py	100.00000% <100.00000%> (ø)
src/trio/_core/_tests/test_guest_mode.py	100.00000% <100.00000%> (ø)
src/trio/_core/_tests/test_instrumentation.py	100.00000% <100.00000%> (ø)
src/trio/_core/_tests/test_run.py	100.00000% <100.00000%> (ø)
src/trio/lowlevel.py	100.00000% <ø> (ø)

[oremanj]

Looks great, thanks!

[Zac-HD]

Thanks @A5rocks!