[cssom] Update WebIDL definition(s) to use new mixin syntax

[tobie]

Hi all!

WebIDL recently introduced dedicated syntax for mixins.

This syntax replaces the [NoInterfaceObject] extended attribute and implements statement which have been deprecated (except for a few legacy uses cases explicitely mentioned in the spec).

You can read more about it here.

In most cases, the changes should be relatively straightforward. The now deprecated:

interface Foo { };

[NoInterfaceObject]  // (Mostly) DEPRECATED
interface Bar { };
Foo implementes Bar; // DEPRECATED

should just be rewritten as:

interface Foo { };

interface mixin Bar { };
Foo includes Bar;

Additonaly, a section on when to use partials and mixins has been added to the spec. It's short and might be worth a read.

It seems the following interfaces in the CSS Object Model (CSSOM) spec are impacted by this change:

• LinkStyle
• ElementCSSInlineStyle

We're sorry for the inconvenience this causes, but our hope is that this ultimately makes things simpler and clearer for everybody.

As always, please feel free to reach out if you have any questions.

Thanks!

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Tracked in: whatwg/webidl#472 | Original pull-request: whatwg/webidl#433