patch 8.2.3967: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more errors to errors.h.
diff --git a/src/if_python3.c b/src/if_python3.c
index db88527..938ab8d 100644
--- a/src/if_python3.c
+++ b/src/if_python3.c
@@ -797,7 +797,7 @@
     if (!hinstPy3)
     {
 	if (verbose)
-	    semsg(_(e_loadlib), libname, load_dll_error());
+	    semsg(_(e_could_not_load_library_str_str), libname, load_dll_error());
 	return FAIL;
     }
 
@@ -809,7 +809,7 @@
 	    close_dll(hinstPy3);
 	    hinstPy3 = 0;
 	    if (verbose)
-		semsg(_(e_loadfunc), py3_funcname_table[i].name);
+		semsg(_(e_could_not_load_library_function_str), py3_funcname_table[i].name);
 	    return FAIL;
 	}
     }
@@ -844,7 +844,7 @@
 	close_dll(hinstPy3);
 	hinstPy3 = 0;
 	if (verbose)
-	    semsg(_(e_loadfunc), "PyUnicode_UCSX_*");
+	    semsg(_(e_could_not_load_library_function_str), "PyUnicode_UCSX_*");
 	return FAIL;
     }