patch 8.2.2843: Vim9: skip argument to searchpairpos() is not compiled

Problem:    Vim9: skip argument to searchpairpos() is not compiled.
Solution:   Handle like searchpair().  Also for search() and searchpos().
diff --git a/src/vim9compile.c b/src/vim9compile.c
index 03aca55..fd32660 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -3285,8 +3285,12 @@
     vim_strncpy(namebuf, *arg, varlen);
     name = fname_trans_sid(namebuf, fname_buf, &tofree, &error);
 
-    // we handle the "skip" argument of searchpair() differently
-    is_searchpair = (varlen == 10 && STRNCMP(*arg, "searchpair", 10) == 0);
+    // We handle the "skip" argument of searchpair() and searchpairpos()
+    // differently.
+    is_searchpair = (varlen == 6 && STRNCMP(*arg, "search", 6) == 0)
+	         || (varlen == 9 && STRNCMP(*arg, "searchpos", 9) == 0)
+	        || (varlen == 10 && STRNCMP(*arg, "searchpair", 10) == 0)
+	        || (varlen == 13 && STRNCMP(*arg, "searchpairpos", 13) == 0);
 
     *arg = skipwhite(*arg + varlen + 1);
     if (compile_arguments(arg, cctx, &argcount, is_searchpair) == FAIL)