Rename find_next_newline to find_newline_no_quit.
src/search.c (find_newline_no_quit): Rename from find_next_newline.
Add commentary.
src/lisp.h (find_newline_no_quit): Rename prototype.
src/xdisp.c (back_to_previous_line_start)
(forward_to_next_line_start, get_visually_first_element)
(move_it_vertically_backward): Callers of find_newline_no_quit changed.
src/indent.c (vmotion): Callers of find_newline_no_quit changed.
src/bidi.c (bidi_find_paragraph_start): Callers of
find_newline_no_quit changed.