patch 9.0.1520: completion for option name includes all bool options

Problem:    Completion for option name includes all bool options.
Solution:   Do not recognize the "noinv" prefix.  Prefix "no" or "inv" when
            appropriate.

src/structs.h

@@ -578,6 +578,12 @@ typedef struct
     buffheader_T sr_old_redobuff;
 } save_redo_T;
 
+typedef enum {
+    XP_PREFIX_NONE,	// prefix not used
+    XP_PREFIX_NO,	// "no" prefix for bool option
+    XP_PREFIX_INV,	// "inv" prefix for bool option
+} xp_prefix_T;
+
 /*
  * used for completion on the command line
  */
@@ -586,6 +592,7 @@ typedef struct expand
     char_u	*xp_pattern;		// start of item to expand
     int		xp_context;		// type of expansion
     int		xp_pattern_len;		// bytes in xp_pattern before cursor
+    xp_prefix_T	xp_prefix;
 #if defined(FEAT_EVAL)
     char_u	*xp_arg;		// completion function
     sctx_T	xp_script_ctx;		// SCTX for completion function