wip: move a11y to its on file

[tanhauhau]

Hi @Rich-Harris i was looking at the issue #820, and I was trying to look for the validate/a11y, and realise you've refactored the a11y validation into nodes/Element.ts in #1721.

I was thinking if I to add more a11y the Element.ts file would be very long, so, I tried to refactor out into a separate file. Would like to know your thoughts about this, before I continue to add more a11y validation.

Thanks

---

• accessible-emoji
• aria-activedescendant-has-tabindex
• aria-proptypes
• click-events-have-key-events
• html-has-lang
• img-redundant-alt
• interactive-supports-focus
• label-has-for
• media-has-caption
• mouse-events-have-key-events
• no-interactive-element-to-noninteractive-role
• no-noninteractive-element-interactions
• no-noninteractive-element-to-interactive-role
• no-noninteractive-tabindex
• no-onchange
• no-redundant-roles
• no-static-element-interactions
• role-has-required-aria-props
• role-supports-aria-props

---

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Tests

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[Rich-Harris]

Thanks — I think this is a good move, yeah. Relatedly, I was thinking we should eventually colocate all the warnings, so that you could do something like this...

component.warn(`a11y-aria-attributes`, attribute, {
  name: this.name
});

...instead of this (the current code):

component.warn(attribute, {
  code: `a11y-aria-attributes`,
  message: `A11y: <${this.name}> should not have aria-* attributes`
});

That would make it much easier to build up some documentation about the various error/warning codes, some of which are slightly inscrutable at present. Is a separate issue though, I just mention it because it's tangentially related.

One nit in this PR: we use snake_case for internal variable names and methods, e.g. noMisplacedScope would be no_misplaced_scope.

[Conduitry]

I'm not against this change, but this PR is so old at this point that it would likely need a lot of work, and I'm trying to chip away at the open items slightly. Closing.