Add ability to skip aggressive vscode.Uri encoding

[heroldev]

This is related to a bug present in mindaro-dev.file-downloader: microsoft/vscode-file-downloader#56, and the relevant pull request to fix it: microsoft/vscode-file-downloader#57

When trying to use this extension to download any file through a URL containing query parameters, the Uri is too aggressively encoded resulting in a 400 Bad Request (and no file downloaded).

A good example:
Original URL: http://localhost:8081/service/rest/v1/search/assets/download?group=org.osgi&name=org.osgi.core&version=4.3.1&maven.extension=jar&maven.classifier
when encoded, becomes
http://localhost:8081/service/rest/v1/search/assets/download?group%3Dorg.osgi%26name%3Dorg.osgi.core%26version%3D4.3.1%26maven.extension%3Djar%26maven.classifier, resulting in a bad request since the query parameters were incorrectly encoded.

This is due to a change in how vscode.Uri.toString() works, where an optional parameter was added that allowed inputted URLs to bypass aggressive encoding (since too many extensions depended on the over-aggressive encoding functionality). However, this breaks query parameters as & and = are encoded, causing URLs to break.

vscode.Uri.toString(true) bypasses this aggressive encoding and allows URLs with query parameters to work.

The issue in specific lies in FileDownloader.ts on line 118:

const downloadStream: Readable = await this._requestHandler.get(
                url.toString(), // right here is the bug, this should be url.toString(true)
                timeoutInMs,
                retries,
                retryDelayInMs,
                headers,
                cancellationToken,
                onDownloadProgressChange
            );

There is already a PR out for fixing this bug: microsoft/vscode-file-downloader#57, however the changes also need to be mirrored to the API so that Typescript programs can take advantage of the new optional parameter. This PR mirrors the necessary changes.