devex: Create and document file selection components

[SuaYoo]

In preparation for #2646

Changes

• Adds new <btrix-file-input> component
• Refactors file upload to use btrix-file-input

Manual testing

1. Log in as crawler
2. Go to "Archived Items"
3. Click "Upload WACZ"
4. Drag non-WACZ file into upload area. Verify file is not displayed
5. Drag WACZ file into upload area. Verify file displays as expected
6. Remove file
7. Click "Browse Files"
8. Choose WACZ file. Verify file displays as expected
9. Continue to upload file. Verify file uploads as expected

Screenshots

Page	Image/video
Archived Items
Storybook / File Input

[emma-sg]

Looks mostly good, but seeing a bug with file selection in Storybook — looking into it currently.

Oh, and a thought about FileListItem.file — should it maybe accept Pick<File, "name" | "size"> instead of just File?

[emma-sg]

Nice, looks good!