patch 8.2.3190: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move error messages to errors.h and give them a clear name.
diff --git a/src/vim9execute.c b/src/vim9execute.c
index b882c4d..73896cb 100644
--- a/src/vim9execute.c
+++ b/src/vim9execute.c
@@ -2337,7 +2337,7 @@
 			else if (dest_type == VAR_LIST
 					       && tv_idx->v_type != VAR_NUMBER)
 			{
-			    emsg(_(e_number_exp));
+			    emsg(_(e_number_expected));
 			    status = FAIL;
 			}
 		    }
@@ -3955,7 +3955,7 @@
 			)
 		{
 		    SOURCING_LNUM = iptr->isn_lnum;
-		    emsg(_(e_number_exp));
+		    emsg(_(e_number_expected));
 		    goto on_error;
 		}
 #ifdef FEAT_FLOAT