Provide a role for file input type

[backwardok]

Description of bug or feature request

There currently isn't an equivalent role for a native <input type="file"> element. The capabilities of what's possible to style for a file input type in browsers is very limited. This results in the frequent desire to create a custom widget that provides file selection for uploads.

Where this can become more complicated from an accessibility standpoint is conveying the state of a custom file input. For example, if the file chosen is invalid, with ARIA 1.2, aria-invalid is no longer supported as a global prop. This makes it invalid to apply aria-invalid to a custom widget that may be using a <button> element for uploading. If there were an equivalent file input role, that role could be explicitly named as an allowed role for aria-invalid and convey the invalid state to the user.

Will this require a change to CORE-AAM?

Will this require a change to the ARIA authoring guide?

[scottaohara]

related: w3c/html-aam#421

[spectranaut]

Discuss at last meeting: https://www.w3.org/2023/05/11-aria-minutes#t04