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/ex_eval.c b/src/ex_eval.c
index 08ba858..6491955 100644
--- a/src/ex_eval.c
+++ b/src/ex_eval.c
@@ -255,7 +255,7 @@
 	    if (elem == NULL)
 	    {
 		suppress_errthrow = TRUE;
-		emsg(_(e_outofmem));
+		emsg(_(e_out_of_memory));
 	    }
 	    else
 	    {
@@ -264,7 +264,7 @@
 		{
 		    vim_free(elem);
 		    suppress_errthrow = TRUE;
-		    emsg(_(e_outofmem));
+		    emsg(_(e_out_of_memory));
 		}
 		else
 		{
@@ -592,7 +592,7 @@
 nomem:
     vim_free(excp);
     suppress_errthrow = TRUE;
-    emsg(_(e_outofmem));
+    emsg(_(e_out_of_memory));
 fail:
     current_exception = NULL;
     return FAIL;
@@ -1639,7 +1639,7 @@
 
 		elem = ALLOC_ONE(struct eslist_elem);
 		if (elem == NULL)
-		    emsg(_(e_outofmem));
+		    emsg(_(e_out_of_memory));
 		else
 		{
 		    elem->saved_emsg_silent = emsg_silent;