Environment
Provide version numbers for the following components (information can be retrieved by running tns info in your project folder or by inspecting the package.json of the project):

• CLI: N/A
• Cross-platform modules: 6.1.0
• Android Runtime: N/A
• iOS Runtime: N/A
• Plugin(s): N/A

Describe the bug
ShorthandProperty instances can't be listened for changes

To Reproduce

    const label = new Label();
    label.style.on("marginLeftChange", () => console.log('marginLeftChange!'));
    label.style.on("marginChange", () => console.log('marginChange!'));
    label.style.marginLeft = 5;
    label.style.margin = 10;

Expected behavior
I expected the two messages to be console logged. Actually only marginLeftChange was logged.

Additional context