utils: avoid using internal _imp.is_frozen()

imp has been deprecated for a long time, and were removed in Python 3.12 . As a
workaround, we started using the internal _imp. That is ugly and risky.

It seems less risky to get the functionality in some other way. Here, we just
inspect if 'origin' of the '__main__' module is set and 'frozen'. That seems to
work and do the same, and might be better than using the internal _imp
directly.

This way of inspecting module attributes seems to work in some test cases, but
it is a risky change. This level of importlib doesn't have much documentation,
a complicated implementation, and we are dealing with some odd use cases.

mercurial/utils/resourceutil.py

@@ -8,7 +8,6 b''
 # GNU General Public License version 2 or any later version.
 
 
-import _imp
 import os
 import sys
 import typing
@@ -32,7 +31,12 b' def mainfrozen():'
     return (
         hasattr(sys, "frozen")  # new py2exe
         or hasattr(sys, "importers")  # old py2exe
-        or _imp.is_frozen("__main__")  # tools/freeze
+        or getattr(
+            getattr(sys.modules.get('__main__'), '__spec__', None),
+            'origin',
+            None,
+        )
+        == 'frozen'  # tools/freeze
     )