feat(a11y): improvements to attachment field

[justynoh]

Problem

Attachment fields had a couple major issues with a11y.

1. It did not announce itself as a link or button to upload.
2. It did not refocus correctly onclick (both upload and remove).
3. It kept repeating the question title on focus of the upload field, which it should not.

Closes #4181

Solution

1. Added additional VisuallyHidden components with more descriptive sentences, and made the components that aren't super accessible aria-hidden.
2. When re-rendering, remove the mergedRefs prop from the enclosing box, so that the the focus will go onto the correct element again.
3. Remove aria-describedby which was causing the dropzone focus to repeat the associated formlabel. This was much too verbose because users will already have heard the form label question before scrolling to the dropzone field.

Breaking Changes

• No - this PR is backwards compatible

Screen.Recording.2022-09-15.at.3.08.05.PM.mov