top: adapt utf8 logic to support extra wide characters

Back when top was refactored to support UTF-8 encoding
it was acknowledged that languages like zh_CN were not
supported. That was because a single 'character' might
require more than a single 'column' when it's printed.

Well I've now figured out how to accommodate languages
like that. My adaptation is represented in this patch.

[ and just in case someone wishes to avoid the extra ]
[ runtime costs, a #define OFF_XTRAWIDE is included. ]

Along the way, I've cleaned up some miscellaneous code
supporting the 'Inspect' feature so that the rightmost
screen column was always used rather than being blank.

[ interestingly, my xterm & urxvt terminal emulators ]
[ are able to split extra wide characters then print ]
[ 1/2 of such graphics in the last column. the gnome ]
[ terminal emulator does not duplicate such behavior ]
[ but prints 1 extra character in same width window. ]

Reference(s):
. Sep, 2017 - original utf8 support
commit 9773c56add

Signed-off-by: Jim Warner <james.warner@comcast.net>

top/top.h

@@ -39,6 +39,7 @@
 //#define OFF_SCROLLBK            /* disable tty emulators scrollback buffer */
 //#define OFF_STDERROR            /* disable our stderr buffering (redirect) */
 //#define OFF_STDIOLBF            /* disable our own stdout _IOFBF override  */
+//#define OFF_XTRAWIDE            /* disable our extra wide multi-byte logic */
 //#define PRETENDNOCAP            /* use a terminal without essential caps   */
 //#define QUICK_GRAPHS            /* use fast algorithm, accept +2% distort  */
 //#define RCFILE_NOERR            /* rcfile errs silently default, vs. fatal */
@@ -553,6 +554,7 @@ typedef struct WIN_t {
 //atic void          sig_resize (int dont_care_sig);
 /*------  Special UTF-8 Multi-Byte support  ------------------------------*/
 /*atic char          UTF8_tab[] = { ... }                                 */
+//atic inline int    utf8_cols (const unsigned char *p, int n);
 //atic int           utf8_delta (const char *str);
 //atic int           utf8_embody (const char *str, int width);
 //atic const char   *utf8_justify (const char *str, int width, int justr);