fix(FileUploaderDropContainer): pass through empty accept attr

[emyarod]

Closes #4519

Previously if the user did not supply any file type restrictions, the resulting validated files array would be empty. This PR adds a check for empty accept attribute on drop events to pass through drag and dropped files when the accept attribute is not specified

This PR also adds a code sandbox example application using the dnd uploader

Changelog

New

• Code Sandbox drag and drop file uploader example

Changed

• accept prop check in validateFiles method
• move max-width rule to drop container label to fix a visual bug where the focus outline extended past the drop area

Testing / Reviewing

• Remove the default accept knob value in storybook
• ensure the component functions as expected

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[Georgegriff]

bit confused did empty accept ever work? if so when was it changed?
Also when would you predict this fix would be available? trying to decide if i should do the mime type work around for now, which will be tricky since we pretty much allow any files to be uploaded

[emyarod]

this PR only affects drag and drop behavior. accept by default only affects the operating system's native file picker, and empty accept becomes *.* in the native file picker.

currently the mime types in accept are followed when the user performs a drag and drop upload, but an empty value for accept will cause an error, which is what this PR should address. in this PR empty accept now allows any file to be uploaded via drag and drop just like it would for the native file picker. until this PR is merged in, if you want to be able to accept all mime types for drag and drop uploading specifically, you would have to pass in mime types to accept or modify the component source to match this PR

[Georgegriff]

@emyarod thanks for the clarity :)

[asudoh]

LGTM 👍 - Thanks @emyarod!

[joshblack]

Seems great, any chance we need to add a test for this or should be good?

[emyarod]

sure I can look into that