Javascript/Typescript style spread operator

[JessieWadman]

Whenever I switch between TypeScript and C#, I find myself missing the spread operator in C#.
Would be nice to have it.

// Arrays
var array1 = new int[] { 1, 2, 3 };
var array2 = new int[] { 4, 5, 6 }; 
var array3 = new int[] { 7, 8, 9 }; 

var union = new int[] { ...array1, ...array2, ...array3[..^2], 10, 11 }; 

// Anonymous objects
// Used to generate a new, anonymous type by combining objects from various sources into a result in an ASP.NET Core controller action
public async Task<ActionResult> Get()
{
  var person = myDb.GetPersonById(1);  // { id: 1, name: "John Doe" }
  var addresses = myDb.GetAddressesById(1); // { addresses: [ { street: "1 Microsoft Way" } ] }
  return Ok(new { ...person, ...addresses }); // { id: 1, name: "John Doe", addresses: [ { street: "1 Microsoft Way" } ] }  
}

[333fred]

Duplicate of #2879 and #3648.