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.

Modules/_opcode.c

@@ -367,7 +367,13 @@ _opcode_get_executor_impl(PyObject *module, PyObject *code, int offset)
                      Py_TYPE(code)->tp_name);
         return NULL;
     }
+#ifdef _Py_TIER2
     return (PyObject *)PyUnstable_GetExecutor((PyCodeObject *)code, offset);
+#else
+    PyErr_Format(PyExc_RuntimeError,
+                 "Executors are not available in this build");
+    return NULL;
+#endif
 }
 
 static PyMethodDef