"Insert before markers" in read_and_insert_process_output properly

"Insert before markers" in read_and_insert_process_output properly

* src/coding.c (setup_coding_system): Initialize it.
(produce_chars, encode_coding, decode_coding_gap):
Obey it in insert_from_gap calls.
(encode_string_utf_8, decode_string_utf_8): Update the other calls
to insert_from_gap to have one new argument (false).

* src/coding.h: New field insert_before_markers.

* src/decompress.c (Fzlib_decompress_region): Here too.

* src/insdel.c (insert_from_gap):
Accept new argument BEFORE_MARKERS (bug#71525) and pass it through
to adjust_markers_for_insert.

* src/lisp.h: Update prototype.

* src/process.c (read_and_insert_process_output):
Set process_coding->insert_before_markers instead of calling
adjust_markers_for_insert.