py/builtinevex: Handle invalid filenames for execfile.

If a non-string buffer was passed to execfile, then it would be passed
as a non-null-terminated char* to mp_lexer_new_from_file.

This changes mp_lexer_new_from_file to take a qstr instead (as in almost
all cases a qstr will be created from this input anyway to set the
`__file__` attribute on the module).

This now makes execfile require a string (not generic buffer) argument,
which is probably a good fix to make anyway.

Fixes issue #12522.

This work was funded through GitHub Sponsors.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

tests/micropython/builtin_execfile.py

@@ -70,5 +70,11 @@ except OSError:
 # Test execfile with a file that does exist.
 execfile("/test_mnt/test.py")
 
+# Test that it only works with string arguments.
+try:
+    execfile(b"aaa")
+except TypeError:
+    print("TypeError")
+
 # Unmount the VFS object.
 os.umount(fs)

tests/micropython/builtin_execfile.py.exp

@@ -3,4 +3,5 @@ open /noexist.py rb
 OSError
 open /test.py rb
 123
+TypeError
 umount