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/spell.c b/src/spell.c
index 0b693c7..46912ff 100644
--- a/src/spell.c
+++ b/src/spell.c
@@ -2137,7 +2137,7 @@
 		    if (ga_grow(&ga, 1) == FAIL)
 		    {
 			ga_clear(&ga);
-			ret_msg = e_outofmem;
+			ret_msg = e_out_of_memory;
 			goto theend;
 		    }
 		    LANGP_ENTRY(ga, ga.ga_len)->lp_slang = slang;