Format and doc changes to bring closer to xterm.c.

Format and doc changes to bring closer to xterm.c.
(w32_char_font_type): New enum.
(Qw32_charset_*, w32_codepage_for_font): Moved to w32fns.c.
(w32_per_char_metric): Use w32_char_font_type instead of unicode_p.
(w32_encode_char): New function.
(x_encode_char): Removed.
(x_get_glyph_and_face_encoding): Use w32_encode_char in place of
x_encode_char and w32_font_is_double_byte.
(x_produce_image_glyph): Use image_ascent.
(x_produce_glyphs): Use new version of w32_per_char_metric and
handle NULL return value. Allow extra line spacing.
(W32_TEXTOUT): Distinguish between Unicode and DBCS text.
(w32_get_glyph_overhangs): Remove unicode_p param. Use
w32_font_type member of glyph instead.
(x_draw_glyph_string): Draw underline and strike-out for BDF fonts.
(fast_find_position): Make sure not to consider rows not visible
in the window.
(w32_read_socket) [WM_MENUSELECT]: Cannot call
w32_menu_display_help with input blocked, as it can abort.
(x_display_and_set_cursor): Choose cursor depending
on buffer-local value of cursor_type.
(x_draw_bar_cursor): Add parameter WIDTH.