(remember_mouse_glyph): New function.

(remember_mouse_glyph): New function.
(w32_mouse_position): Use it.
(note_mouse_movement): If the mouse moved off the glyph, remember its
new position.

Sync with xterm.c:
(notice_overwritten_cursor): Renamed from note_overwritten_text_cursor.
Rewritten to take glyph widths into account.
(x_y_to_hpos_vpos): Add parameter BUFFER_ONLY_P.
(fast_find_string_pos): New function.
(fast_find_position): Return the correct vpos.  Add parameter STOP.
In the final row, stop before glyphs having STOP as object.
Don't consider glyphs that are not from a buffer.
(fast_find_position) [0]: Add a presumably more correct version for after 21.1.
(expose_window_tree, expose_frame): Don't compute intersections here.
(expose_window): Do it here instead.
(expose_window_tree, expose_window, expose_line): Return 1 when
overwriting mouse-face.
(expose_window): If W is the window currently being updated, mark
the frame garbaged.
(expose_frame): If mouse-face was overwritten, redo it.
(x_use_underline_position_properties): New variable.
(syms_of_xterm): DEFVAR_BOOL it.
(x_draw_glyph_string): Add comment to use it in future.
(x_draw_glyph_string): Restore clipping after drawing box.
Fix a computation of the underline position.
(w32_get_glyph_string_clip_rect): Minor cleanup.
(x_fill_stretch_glyph_string): Remove an assertion.
(x_produce_glyphs): Don't convert multibyte characters
to unibyte characters in unibyte buffers.
(cursor_in_mouse_face_p): New function.
(x_draw_stretch_glyph_string): Use it to choose a different GC
when drawing a cursor within highlighted text.  Don't draw
background again if it has already been drawn.
(x_draw_glyph_string_box): Don't draw a full-width
box just because the glyph row's full_width_p flag is set.
(x_draw_glyphs): Fix computation of rightmost x for full-width rows.
(x_dump_glyph_string): Put in #if GLYPH_DEBUG.
(w32_draw_relief_rect): Extend left shadow to the bottom and left;
change bottom shadow accordingly. Some cleanup.
(x_update_window_end): Handle overwritten mouse face
also for tool bar windows.
(show_mouse_face): Set the glyph row's mouse_face_p flag also when
DRAW is DRAW_IMAGE_RAISED.
(clear_mouse_face): Return 1 if text with mouse face was
actually redrawn.  Make the function static.  Reset
dpyinfo->mouse_face_overlay otherwise note_mouse_highlight might
optimize away highlighting if we pass over that same overlay again.
(note_mouse_highlight): Call mouse_face_overlay_overlaps
to detect a case where we have to highlight a different region
despite not having left the currently highlighted region.
Set mouse_face_overlay in the x_display_info.  Avoid changing the
mouse pointer shape when show_mouse_face has already done it, or
there is no need.  Handle mouse-face and help-echo in strings.
(glyph_rect): New function.
(w32_mouse_position): Use it to raise the threshold for mouse
movement event generation.
(w32_initialize_display_info): Initialize the x_display_info's
mouse_face_overlay.
(w32_set_vertical_scroll_bar): Don't clear a zero height or width area.
(w32_set_vertical_scroll_bar, x_scroll_bar_create): Don't configure
a widget to zero height.