Fix broken JS on Cloud uploader when changing dirs

[timkelty]

Following #14439, a JS error was thrown when navigating directories.
This is because AssetIndex was calling .fileupload(), which can't be assumed, as only hte core Uploader uses the jquery uploader plugin.

Changes

• When selecting source, make onSelectSource fire before onSourcePathChange to be less awkward.
• With onSelectSource fired first, we can be certain out uploader is created by the time we get to onSourcePathChange
• Don't call fileupload methods if the plugin wasn't instantiated (eg if uploading is disabled)
• Eliminate duplicate inputs by settingreplaceFileInput = false, which is only needed for very old iframe uploading.

History

• this was reported: [4.x]: Asset Browser crashes when quickly switching between sources with different upload permissions #14403
• first fix (@brandon): af652db
• but then it caused this: [4.x]: Uploading files via asset modal > upload files and assets index > upload files is broken #14438
• second fix (@i-just ): Bugfix/14438 uploading files uploader errors #14439

Test cases

• permissions
  • create 2 volumes
  • user can do everything for vol1
  • user can only view vol2
  • vol1 has one subfolder
  • go to vol1 > subfolder & upload a file - all good
  • go to vol2 - upload button is disabled and you can’t upload - all good
  • go to vol1, you should be deep linked into the subfolder (cause that’s where you were last); try to upload a file
• Assets page
  • upload button
  • drag to upload
• Assets field
  • select via modal
  • upload directly
  • upload directly via drag