Support Downloading and Uploading files to HTML pages

[NSPC911]

Check for existing issues

• Completed

Describe the feature

Currently ACode is unable to upload files to <input type=file> elements as it currently just bugs out without any options to upload.

Downloading also straight up doesn't work, there is no popup asking to download it where or open it with any app

Please add this, I need it for fixing bugs on my website related to files!

Todo

• upload <input type=file> fix: fallback to */* when accept attribute is absent in input type="file" #1154
• download

If applicable, add mockups / screenshots to help present your vision of the feature

NIL, no UI needed, System UI is enough