[5.x] Conditional fields in asset blueprints

[daun]

Make native asset data (width, height, filename, etc) available as hidden fields inside the asset editor component.

This enables field conditions inside asset blueprints against native asset data, e.g. to show fields for some filetypes only.

Closes statamic/ideas#1136

Example use case

The example below will show an Autoplay toggle for all videos shorter than a minute:

fields:
  -
    handle: autoplay
    field:
      type: toggle
      display: Autoplay
      if:
        extension: mp4
        duration: '<= 60'

Required changes

• Asset Resource class: Append mimetype and duration in Asset resource
• Asset Editor component: Create hidden fields for asset data, merge asset data with blueprint field data

Notes

• Hiding the fields in the blueprint also ensures their data isn't sent along when saving the asset
• The mime type field is available as mimeType — should this be snake-cased to mime_type to match the yaml key?