mapUriToFile has no implementation for `http` / `https` schemes

https://github.com/apache/cordova-android/blob/954d3e0e7542356e6ea995ddc75dcb1db8bb36cc/framework/src/org/apache/cordova/CordovaResourceApi.java#L149-L173

The `cordova-plugin-file-transfer` plugin utilizes this method to map a uri value such as `http://localhost/__cdvfile_persistent__/testFile.txt` to a local file url, when using the file transfer's download API. However because this API does not handle the `http` scheme, it returns a Null, which eventually leads to a `NullPointerException` and failing unit tests.

the `testFile.txt` url comes from the [following code](https://github.com/apache/cordova-plugin-file-transfer/blob/2465f508adfadd5be4a8ea9ecd1ca01779164ea2/tests/tests.js#L333-L335):

```javascript
this.root = this.persistentRoot;
this.fileName = 'testFile.txt';
this.localFilePath = this.root.toURL() + this.fileName;
```
Where `this.persistentRoot` [resolved by](https://github.com/apache/cordova-plugin-file-transfer/blob/2465f508adfadd5be4a8ea9ecd1ca01779164ea2/tests/tests.js#L215-L225):

```javascript
window.requestFileSystem(
LocalFileSystem.PERSISTENT,
DEFAULT_FILESYSTEM_SIZE,
function (fileSystem) {
specContext.persistentRoot = fileSystem.root;
done();
},
function () {
throw new Error('Failed to initialize persistent file system.');
}
);
```

I'm raising the issue here because the method in question is located inside cordova-android, but it's unclear if the solution is to update `mapUriToFile` support this use case, or if the file transfer plugin should expect `file://` urls instead of http:// urls.

Start with framework/src/org/apache/cordova/CordovaResourceApi.java at lines 149-173 and trace the mapUriToFile URI contract. Reproduce the file-transfer path described in tests/tests.js at lines 215-225 and 333-335, then determine whether Android or the plugin should own http/https handling; done means the null result, NPE, and failing tests are resolved under the agreed contract.

Written by the indexing model from the issue text.