[Errors] merged interface declarations with conflicting heritage specifications

[mhegazy]

//== tests/cases/compiler/conflictingMemberTypesInBases.ts (1 errors) ====
interface A {
    m: string;
}
interface B extends A {
}
interface C {
    m: number;
}
interface D extends C {
}

interface E extends B { } // Error here for extending B and D
//!!! Interface 'E' cannot simultaneously extend types 'B' and 'D':
//!!! Named properties 'm' of types 'B' and 'D' are not identical.
interface E extends D { } // No duplicate error here

Expected: errors as above
Actual: no errors

[ahejlsberg]

Already fixed.