Rename find_next_newline to find_newline_no_quit.

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.