[typescript] Offer IntelliSense suggestions based on method parameter or local type

[mjbvz]

From @rstarkov on November 7, 2017 12:25

It would be useful if IntelliSense offered suggestions based on the expected type of the expression being edited. Consider the following examples:

function Foo(thing: Namespace.Stuff.SomeClass) { ... }

Foo(new |
        ^ here

let x: Namespace.Stuff.SomeClass;
x = new |
        ^ here

In these cases, "Namespace.Stuff.SomeClass" should be offered by IntelliSense at the indicated positions.

This behaviour would also be handy for enums: the enum type could be offered in the same contexts as above (without the new keyword obviously).

For enums there's another scenario where this would be handy, namely when I'm comparing an enum-typed local or parameter - IntelliSense should offer the enum type for autocompletion after I type the comparison operator.

Copied from original issue: microsoft/vscode#37771

[mjbvz]

Moved over to TypeScript for further discussion

[mhegazy]

Made a related comment a few days ago in #16864 (review)