gh-118335: Configure Tier 2 interpreter at build time (#118339)

The code for Tier 2 is now only compiled when configured
with `--enable-experimental-jit[=yes|interpreter]`.

We drop support for `PYTHON_UOPS` and -`Xuops`,
but you can disable the interpreter or JIT
at runtime by setting `PYTHON_JIT=0`.
You can also build it without enabling it by default
using `--enable-experimental-jit=yes-off`;
enable with `PYTHON_JIT=1`.

On Windows, the `build.bat` script supports
`--experimental-jit`, `--experimental-jit-off`,
`--experimental-interpreter`.

In the C code, `_Py_JIT` is defined as before
when the JIT is enabled; the new variable
`_Py_TIER2` is defined when the JIT *or* the
interpreter is enabled. It is actually a bitmask:
1: JIT; 2: default-off; 4: interpreter.

Python/sysmodule.c

@@ -2165,8 +2165,10 @@ static PyObject *
 sys__clear_internal_caches_impl(PyObject *module)
 /*[clinic end generated code: output=0ee128670a4966d6 input=253e741ca744f6e8]*/
 {
+#ifdef _Py_TIER2
     PyInterpreterState *interp = _PyInterpreterState_GET();
     _Py_Executors_InvalidateAll(interp, 0);
+#endif
     PyType_ClearCache();
     Py_RETURN_NONE;
 }