Accessibility: Hide hidden file upload button from assistive technologies

[shrivastavanolo]

The .wp-uploader-browser container and its "Select Files" button were being hidden from sighted users via off-screen positioning, but remained reachable by screen readers and keyboard navigation. This caused screen reader users to encounter focusable "Select Files" buttons with no visible context.

Changes display:none instead, which hides the container from all users including assistive technologies until it is actually needed.

Trac ticket: https://core.trac.wordpress.org/ticket/47144

Use of AI Tools

AI assistance: Yes
Tool(s): Claude
Model(s): Opus 4.7
Used for: Initial code skeleton; final implementation was tested and edited by me.

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