Fix: fileCopyUri should include the URI schema

[kidroca]

Summary

Make the fileCopyUri be a URI string and include the schema prefix (usually file:/)

• fixes fileCopyUri has file:// prefix on iOS but doesn't on Android #526

A URI should begin with the schema prefix
In iOS fileCopyUri already works that way
Missing the schema prefix causes a problem when you try to use fileCopyUri with fetch to upload a file

Why .toURI().toString()

This was the only method I've found that returned the schema as part of the string
The same thing is used in RN image picker here

Difference between file:/ and file:///

Since on iOS fileCopyUri is returned with a file:/// prefix - you might be wondering if this is a problem.
According to wikipedia file:/ and file:/// are the same thing: https://en.wikipedia.org/wiki/File_URI_scheme#How_many_slashes.3F

Test Plan

I've manually tested the changes in the example app and in an external app

Before (no file:/ prefix for fileCopyUri)

 LOG  [
  {
    "size": 3028,
    "fileCopyUri": "/data/user/0/com.example.reactnativedocumentpicker/cache/7246f3d1-815b-45fa-86ce-a420da059da4/sample.pdf",
    "name": "sample.pdf",
    "type": "application/pdf",
    "uri": "content://com.android.providers.downloads.documents/document/18"
  }
]

After

 LOG  [
  {
    "size": 3028,
    "fileCopyUri": "file:/data/user/0/com.example.reactnativedocumentpicker/cache/d87a83fe-e393-40f2-9f5f-f3ebe2641974/sample.pdf",
    "name": "sample.pdf",
    "type": "application/pdf",
    "uri": "content://com.android.providers.downloads.documents/document/18"
  }
]

Sample video (after) in our app:

2022-01-18_21-40-23.mp4

• You can see that we used to test whether fileCopyUri starts with a scheme and added file: if it didn't
• Now that's no longer necessary

Sample for the same in iOS

No iOS change, but just showing how it already works there:

What's required for testing (prerequisites)?

This can be manually tested in the example app

What are the steps to reproduce (after prerequisites)?

1. Use the example app on Android
2. Use the "Open Picker For Single File Selection" button
   (Or any button that passes a copyTo Document Picker Option)
3. Select a file
4. See the displayed fileCopyUri - it should contain the URI schema in the beginning e.g. file:/

Compatibility

OS	Implemented
iOS	✅
Android	✅

Checklist

• I have tested this on a device and a simulator
• n/a I added the documentation in README.md
• n/a I updated the typed files (TS and Flow)

[vonovak]

thank you for the PR and the comprehensive description! :)