Add a Nobr terminfo capability to tell tmux the terminal does not use

bright colours for bold (makes a difference to how tmux applies palette
differences). From Damien Tardy-Panis in GitHub issue 3301.

tmux.1

@@ -6430,6 +6430,10 @@ These are set automatically if the
 capability is present.
 .It Em \&Hls
 Set or clear a hyperlink annotation.
+.It Em \&Nobr
+Tell
+.Nm
+that the terminal does not use bright colors for bold display.
 .It Em \&Rect
 Tell
 .Nm

tmux.h

@@ -514,6 +514,7 @@ enum tty_code_code {
 	TTYC_KUP6,
 	TTYC_KUP7,
 	TTYC_MS,
+	TTYC_NOBR,
 	TTYC_OL,
 	TTYC_OP,
 	TTYC_RECT,

tty-term.c

@@ -247,6 +247,7 @@ static const struct tty_term_code_entry tty_term_codes[] = {
 	[TTYC_KUP6] = { TTYCODE_STRING, "kUP6" },
 	[TTYC_KUP7] = { TTYCODE_STRING, "kUP7" },
 	[TTYC_MS] = { TTYCODE_STRING, "Ms" },
+	[TTYC_NOBR] = { TTYCODE_STRING, "Nobr" },
 	[TTYC_OL] = { TTYCODE_STRING, "ol" },
 	[TTYC_OP] = { TTYCODE_STRING, "op" },
 	[TTYC_RECT] = { TTYCODE_STRING, "Rect" },

tty.c

@@ -2690,12 +2690,14 @@ tty_check_fg(struct tty *tty, struct colour_palette *palette,
 
 	/*
 	 * Perform substitution if this pane has a palette. If the bright
-	 * attribute is set, use the bright entry in the palette by changing to
-	 * the aixterm colour.
+	 * attribute is set and Nobr is not present, use the bright entry in
+	 * the palette by changing to the aixterm colour
 	 */
 	if (~gc->flags & GRID_FLAG_NOPALETTE) {
 		c = gc->fg;
-		if (c < 8 && gc->attr & GRID_ATTR_BRIGHT)
+		if (c < 8 &&
+		    gc->attr & GRID_ATTR_BRIGHT &&
+		    !tty_term_has(tty->term, TTYC_NOBR))
 			c += 90;
 		if ((c = colour_palette_get(palette, c)) != -1)
 			gc->fg = c;