[WiP] "role attribute has valid value" for focusable elements draft

[Jym77]

Drafting a rule for "role attribute has valid value" specialised on focusable elements that can be considered as UI components and thus maps to 4.1.2

Closes issue(s):

• N/A

Need for Final Call:
This will require a 2 weeks Final Call (new rule)

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[WilcoFiers]

This looks promising.

[Jym77]

Closing since this is not necessary after #1537.