patch 8.2.3830: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more error messages to errors.h.
diff --git a/src/diff.c b/src/diff.c
index 92a4d9f..45c5e0b 100644
--- a/src/diff.c
+++ b/src/diff.c
@@ -173,7 +173,7 @@
 	    return;
 	}
 
-    semsg(_("E96: Cannot diff more than %d buffers"), DB_COUNT);
+    semsg(_(e_cannot_diff_more_than_nr_buffers), DB_COUNT);
 }
 
 /*
@@ -1081,7 +1081,7 @@
     {
 	if (io_error)
 	    emsg(_("E810: Cannot read or write temp files"));
-	emsg(_("E97: Cannot create diffs"));
+	emsg(_(e_cannot_create_diffs));
 	diff_a_works = MAYBE;
 #if defined(MSWIN)
 	diff_bin_works = MAYBE;
@@ -1636,7 +1636,7 @@
 	fd = mch_fopen((char *)dout->dout_fname, "r");
 	if (fd == NULL)
 	{
-	    emsg(_("E98: Cannot read diff output"));
+	    emsg(_(e_cannot_read_diff_output));
 	    return;
 	}
     }
@@ -2625,7 +2625,7 @@
     idx_cur = diff_buf_idx(curbuf);
     if (idx_cur == DB_COUNT)
     {
-	emsg(_("E99: Current buffer is not in diff mode"));
+	emsg(_(e_current_buffer_is_not_in_diff_mode));
 	return;
     }
 
@@ -2646,7 +2646,7 @@
 	    if (found_not_ma)
 		emsg(_("E793: No other buffer in diff mode is modifiable"));
 	    else
-		emsg(_("E100: No other buffer in diff mode"));
+		emsg(_(e_no_other_buffer_in_diff_mode));
 	    return;
 	}
 
@@ -2656,7 +2656,7 @@
 		    && curtab->tp_diffbuf[i] != NULL
 		    && (eap->cmdidx != CMD_diffput || curtab->tp_diffbuf[i]->b_p_ma))
 	    {
-		emsg(_("E101: More than two buffers in diff mode, don't know which one to use"));
+		emsg(_(e_more_than_two_buffers_in_diff_mode_dont_know_which_one_to_use));
 		return;
 	    }
     }
@@ -2679,7 +2679,7 @@
 	buf = buflist_findnr(i);
 	if (buf == NULL)
 	{
-	    semsg(_("E102: Can't find buffer \"%s\""), eap->arg);
+	    semsg(_(e_cant_find_buffer_str), eap->arg);
 	    return;
 	}
 	if (buf == curbuf)
@@ -2687,7 +2687,7 @@
 	idx_other = diff_buf_idx(buf);
 	if (idx_other == DB_COUNT)
 	{
-	    semsg(_("E103: Buffer \"%s\" is not in diff mode"), eap->arg);
+	    semsg(_(e_buffer_str_is_not_in_diff_mode), eap->arg);
 	    return;
 	}
     }