Relax index signature checks for type any

[ahejlsberg]

With this change, a type without an index signature is considered related to a type with an index signature if the type of that index signature is any. For example:

var x: { foo: number, [x: string]: any };
let y = { foo: 1, baz: 2 }; 
x = y;  // No longer an error

The assignment x = y was previously considered an error because y has no index signature. However, given that an index signature of type any doesn't actually constrain properties in the type, the assignment is now permitted.

This issue was originally reported by @joewood here.

[RyanCavanaugh]

Use isTypeAny

[ahejlsberg]

That would just add function call and a redundant null check.

[RyanCavanaugh]

👍

[ahejlsberg]

@JsonFreeman Agreed.

[JsonFreeman]

👍