Issue better error message for binary operations between numbers and bigints

[DanielRosenwasser]

declare let x: bigint;
declare let y: number;

x + y;
y + x;
x - y;
y - x;
x * y;
y * x;
x / y;
y / x;

x += y;
y += x;

Each of these gives an error like "Operator '{0}' cannot be applied to types '{1}' and '{2}'". It should somehow tell the user that the number argument needs to be converted to a bigint.

[weswigham]

For the non-assignments: "Operator '{0}' cannot be applied to types '{1}' and '{2}'". Consider wrapping the '{3}' side of the operator with a call to 'BigInt'.?

[m-henderson]

@DanielRosenwasser @weswigham did you guys decide on what you would like the diagnostics message to say?