[File uploader] update bugs in the documentation

[laurenmrice]

Acceptance criteria

There are a few bugs that were found in the docs in relation to the Figma Audit that was conducted for code snippet that we need to resolve.

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Usage tab

Loading states section

• Success should be renamed to "complete".

Style tab

Color section

• The background color of the file should be using the $layer color token, not field.

Interactive states section

• The word "Uploaded" should be “Complete” in the table.
• Change the state to say "Hover + Drag" for the zone area
• The disabled state should specify the drop zone border as $border-disabled.
• The captions for the images should be improved.
  • First image could say: Interactive states of a file item
  • Second image could say: Interactive states of a drag and drop file uploader