[Feature] - expand typedef - combine multiple types into a new type

[dinbtechit]

It would be nice if we could expand typedef to combine multiple types into a new type, similar to typescript.

Current Scenario

dynamic getIntOrDouble() {
  // this method can return either Int or double. 
  // But it could also return anything and the compiler would not complain about it.
}

Proposed Scenario

Pseudo Code:

typedef MyNumber = int | double;

Usage:

MyNumber getIntOrDouble() {
 // Now this must return an int or a double. Or else you get a compile error.
}

[lrhn]

That sounds like union types: #1222.