Refactor telemetry code

[DonJayamanne]

When there's an error just send:

• Original event
• Error location
• Drop other data items

[DonJayamanne]

Prescribed Solution:

• Modify https://github.com/Microsoft/vscode-python/blob/e28d1489e74b878ad46a8863d069197ec065d700/src/client/telemetry/index.ts
• sample solution

    if (ex && (eventName as any) !== 'ERROR') {
        customProperties.originalEventName = eventName as any as string;
        const data = { stackTrace: customProperties.stackTrace, originalEventName: eventName };
        reporter.sendTelemetryEvent('ERROR', data, measures);
    }

[ericsnowcurrently]

@DonJayamanne, how to validate this?