Use a strong hash (SHA256) when transmitting VS Code project identifiers in telemetry

[amcasey]

The projectid property on event typescript/projectinfo has been suppressed because it contains weakly-hashed (MD5) customer content (a file path). If we want to regain this functionality (project identification), we will need to introduce a new property (because we have to continue to suppress telemetry from old clients) containing a strongly-hashed (SHA256) value.

Note that the actual code change might be in https://github.com/Microsoft/vscode, since that's where our extension lives.

[amcasey]

When this is done, we'll also have to add a GDPR classification for the new property before we can start consuming it.