Fix bug #14575 with window-specific overlays with display props.

Fix bug #14575 with window-specific overlays with display props.

 src/bidi.c (bidi_fetch_char): Accept additional argument, the window
 being displayed, and pass it to compute_display_string_pos.
 (bidi_level_of_next_char, bidi_resolve_explicit_1)
 (bidi_paragraph_init): All callers changed.
 src/xdisp.c (init_from_display_pos, init_iterator)
 (handle_single_display_spec, next_overlay_string)
 (get_overlay_strings_1, reseat_1, reseat_to_string)
 (push_prefix_prop, Fcurrent_bidi_paragraph_direction): Set
 bidi_it.w member from it->w.
 (compute_display_string_pos): Accept additional argument, the
 window being displayed, and pass it to Fget_char_property.
 src/dispextern.h (struct bidi_it): New member w, the window being
 displayed.
 (compute_display_string_pos): Adjust prototype.