[js] TextMetrics.actualBoundingBoxLeft not available

[TextMetrics.hx](https://github.com/HaxeFoundation/haxe/blob/71e286099fc39a81cee62af2807d4015e639f635/std/js/html/TextMetrics.hx) does not have the latest fields defined in [the API](https://developer.mozilla.org/en-US/docs/Web/API/TextMetrics).

This might be because the latest WebIDLs refresh (https://github.com/HaxeFoundation/haxe/pull/7354) was done in 2018.

Can we have the API updated?

@haxiomic are you planning to do this (saw you added yourself to similar issues like https://github.com/HaxeFoundation/haxe/issues/10146).

If this is documented somewhere I can try to do it but it doesn't seem trivial.