[display] @position on assignment pattern declaration

[Gama11]

import haxe.ds.Option;

class Main {
	public static function main() {
		switch (Some(Some("foo"))) {
			case Some(inner = Some(_)):
				inner;
			case _:
		}
	}
}

I originally thought this was the same as #6381, I guess not though. Requesting @position on the usage in line 7 works:

> haxe --display Main.hx@143@position
<list>
<pos>...\source\Main.hx:6: characters 14-19</pos>
</list>

If you instead do it on the "declaration" the line before, you just get an empty list:

> haxe --display Main.hx@120@position
<list>
</list>

Of course it's a bit silly to request the position of the declaration when you're already there, but vshaxe's rename relies on this, plus it seems to work everywhere else.