Update tree-sitter subroutine in Fsubst_char_in_region

Update tree-sitter subroutine in Fsubst_char_in_region

Some explanation: Fsubst_char_in_region used to have a branch,
one branch path calls replace_range, one branch path modifies
the buffer directly.  replace_range already calls
treesit_record_change within it, so we needed to make sure we
only call treesit_record_change in the other branch path.

After I added the call to treesit_record_change, some changes
are made to Fsubst_char_in_region, and the branch was removed.
So no wonder Stefan had the confusion and wrote the FIXME note.

Now that the branch is gone, we can indeed call
treesit_record_change in the end like signal_after_change.

* src/editfns.c (Fsubst_char_in_region): Move to end.

(cherry picked from commit 3c47139b8f602286a8c5c5ca72431b933b4f2a23)