Include gdscript warning name in the warning message.
Include gdscript warning name in the warning message.

Occasionally you want to ignore a warning with a `warning-ignore`
comment, and you have to go into the settings to look up what the
actual name of the warning is. This patch appends the warning name to
the end of the warning so you know what string to use to ignore it,
similar to other linters like pylint.

For example

```
"The signal 'blah' is declared but never emitted.";
```

is now

```
"The signal 'blah' is declared but never emitted. (UNUSED_SIGNAL)";
```

(cherry picked from commit de3ad3b30ecb8de1aa112df7d61630102f077b5b)

ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot