html: Fix broken $dom_xxx field members

[rakudrama]

Some fields have $dom_ names. This won't work.

  /** @­domName HTMLElement.children */
  final HTMLCollection $dom_children;

  /** @­domName HTMLElement.className */
  String $dom_className;

Suggestion: add native renaming to field declarations:

  String $dom_className native 'className';

This will require fixing frog and dart2js to parse the construct and pass through the js name.
The benefit to the compiler is that it now knows 'className' is special so should not be used as the js name of a Dart field.

It would be possible to use getters and setters with frog-style native bodies.
This will be a net performance loss in frog since there is no inlining.
It also creates more frog-style bodies that will need to eventually be rewritten.

[rakudrama]

Marked this as blocking #2777.

[rakudrama]

I misread the code.
It looks like the all the relevant code is implemented as getters.

I'm closing this issue since they are not 'broken'.

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Added Priority-Medium, Invalid labels.