Add PyInterpreterState.runtime field: reference to the _PyRuntime
global variable. This field exists to not have to pass runtime in
addition to tstate to a function.  Get runtime from tstate:
tstate->interp->runtime.

Remove "_PyRuntimeState *runtime" parameter from functions already
taking a "PyThreadState *tstate" parameter.

_PyGC_Init() first parameter becomes "PyThreadState *tstate".

* Rename PyThreadState_DeleteCurrent()
  to _PyThreadState_DeleteCurrent()
* Move it to the internal C API

Co-Authored-By: Carol Willing <carolcode@willingconsulting.com>

Only AttributeError should be silenced.

In a subinterpreter, spawning a daemon thread now raises an
exception. Daemon threads were never supported in subinterpreters.
Previously, the subinterpreter finalization crashed with a Pyton
fatal error if a daemon thread was still running.

* Add _thread._is_main_interpreter()
* threading.Thread.start() now raises RuntimeError if the thread is a
  daemon thread and the method is called from a subinterpreter.
* The _thread module now uses Argument Clinic for the new function.
* Use textwrap.dedent() in test_threading.SubinterpThreadingTests

This reverts commit 396e0a8d9dc65453cb9d53500d0a620602656cfe.

https://bugs.python.org/issue36818

Automatically replace
tp_print -> tp_vectorcall_offset
tp_compare -> tp_as_async
tp_reserved -> tp_as_async

_thread.start_new_thread() now logs uncaught exception raised by the
function using sys.unraisablehook(), rather than sys.excepthook(), so
the hook gets access to the function which raised the exception.