vi: don't expandtab when we're in command mode.

[Todd C . Miller]

Otherwise you can't search for a tab unless you ^V escape it.

>From nvi2:
https://github.com/lichray/nvi2/commit/0ef1c824648bcfe9f831a9607cb465b18e313d1d

Index: vi/v_txt.c
===================================================================
RCS file: /cvs/src/usr.bin/vi/vi/v_txt.c,v
retrieving revision 1.34
diff -u -p -u -r1.34 v_txt.c
--- vi/v_txt.c  30 Apr 2020 10:40:21 -0000      1.34
+++ vi/v_txt.c  13 Apr 2021 14:18:23 -0000
@@ -1214,7 +1214,8 @@ leftmargin:               tp->lb[tp->cno - 1] = ' ';
                hexcnt = 1;
                goto insq_ch;
        case K_TAB:
-               if (quote != Q_VTHIS && O_ISSET(sp, O_EXPANDTAB)) {
+               if (sp->showmode != SM_COMMAND && quote != Q_VTHIS &&
+                   O_ISSET(sp, O_EXPANDTAB)) {
                        if (txt_dent(sp, tp, O_TABSTOP, 1))
                                goto err;
                        goto ebuf_chk;