Proposal: Interfaces should allow duplicated members

[ENikS]

Allow duplicated members in multiple interface declarations, as long as they are identical. Optional compiling warnings are acceptable, to assist developers to remove redundant codes at convenient time.

This should not generate any errors, example:

shim.d.ts

interface Symbol {
    toString(): string;
    valueOf(): Object;
    [Symbol.toStringTag]: string;
}

es6.d.ts

...
interface Symbol {
    /** Returns a string representation of an object. */
    toString(): string;

    /** Returns the primitive value of the specified object. */
    valueOf(): Object;

    [Symbol.toStringTag]: string;
}
...

[mhegazy]

I do not think we need a new issue for this. issue #3215 seems like a fine place to keep the discussion going.