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

Format and doc changes to bring closer to xfns.c.
(VIETNAMESE_CHARSET): Define if not defined in system headers.
(Qline_spacing, Qcenter): New variables.
(Qw32_charset_*, w32_codepage_for_font): Moved from w32term.c.
(x_set_line_spacing): New function.
(x_set_frame_parameters): Use FRAME_NEW_WIDTH, FRAME_NEW_HEIGHT macros.
(x_specified_cursor_type): New function.
(x_set_cursor_type): Use it.
(x_set_name, x_set_title): Use ENCODE_SYSTEM to encode titlebar and
icon strings.
(validate_x_resource_name, x_get_resource_string): Measure lengths
of external strings in bytes.
(w32_wnd_proc) [WM_MEASURE_ITEM]: Avoid calling
GetTextExtentPoint32 with NULL title.
(Fx_create_frame): Initialize Qline_spacing.
(w32_load_system_font): Initialize font->double_byte_p.
(x_to_w32_charset): Use Vw32_charset_info_alist.
(Image, busy cursor, tooltip functions): Merged changes from
xfns.c. Not yet functional on Windows.