Revise Upload Blobs dialog to avoid using Node APIs

[craxal]

The Upload Blobs dialog currently offloads using any Node APIs to an extension provider in order to use Node APIs to manipulate paths. However, we want to avoid this indirection entirely if possible.

Ideas:

• Display a list of full file paths as returned by the native file dialog.
• Provide an alternate API that returns the root directory and base names of the files.