html: fix $dom_$dom_ methods

[rakudrama]

There are some weirdly named members. Fix the double-$dom-ing.

  // From SVGStylable

  SVGAnimatedStringImpl get $dom$dom_svgClassName() native "return this.className;";

[rakudrama]

Marked this as blocking #2777.

[vsmenon]

Removed Priority-Medium label.
Added Priority-High label.

[rakudrama]

Fixed r7213

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Added Fixed label.