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_python.c b/src/if_python.c
index 1b7ff76..22c2f0c 100644
--- a/src/if_python.c
+++ b/src/if_python.c
@@ -690,7 +690,7 @@
     if (!hinstPython)
     {
 	if (verbose)
-	    semsg(_(e_loadlib), libname, load_dll_error());
+	    semsg(_(e_could_not_load_library_str_str), libname, load_dll_error());
 	return FAIL;
     }
 
@@ -702,7 +702,7 @@
 	    close_dll(hinstPython);
 	    hinstPython = 0;
 	    if (verbose)
-		semsg(_(e_loadfunc), python_funcname_table[i].name);
+		semsg(_(e_could_not_load_library_function_str), python_funcname_table[i].name);
 	    return FAIL;
 	}
     }
@@ -719,7 +719,7 @@
 	close_dll(hinstPython);
 	hinstPython = 0;
 	if (verbose)
-	    semsg(_(e_loadfunc), "PyUnicode_UCSX_*");
+	    semsg(_(e_could_not_load_library_function_str), "PyUnicode_UCSX_*");
 	return FAIL;
     }