[3.12] gh-126742: Add _PyErr_SetLocaleString, use it for gdbm & dlerror messages (GH-126746)

[picnixz]

• Add a helper to set an error from locale-encoded char*
• Use the helper for gdbm & dlerror messages
  (cherry picked from commit 7303f06)

Co-authored-by: Bénédikt Tran 10796600+picnixz@users.noreply.github.com
Co-authored-by: Victor Stinner vstinner@python.org

• Issue: Allow to set non-UTF8 exception messages #126742

[serhiy-storchaka]

Were there other conflicts besides a tab character?

[picnixz]

Were there other conflicts besides a tab character?

There were two conflicts:

• One in the test_dbm where test_clear() was not present in the 3.12 branch.
• One in pycore_pyerrors.h where _PyErr_Format had PyObject* instead of PyObject *.