Index signature parameter should be able to accept types derived from 'string' or 'number'

[garkin]

TypeScript Version: 2.4.2 / nightly (2.5.0-dev.20170727)

Code

type EntityId = number;
const entityMap: { [id: EntityId]: number | undefined } = {};  // error

enum SomeEnum { A, B, C }
const someEnumMap: { [id: SomeEnum]: number | undefined } = {};  // error

const enum ConstEnum { A, B, C }
const constEnumMap: { [id: ConstEnum]: number | undefined } = {};  // error

Playground

Expected behavior: Succesfull compilation.

Actual behavior: Getting an error:

index.ts(2,21): error TS1023: An index signature parameter type must be 'string' or 'number'.
index.ts(5,23): error TS1023: An index signature parameter type must be 'string' or 'number'.
index.ts(8,24): error TS1023: An index signature parameter type must be 'string' or 'number'.

[kitsonk]

Duplicate of #2491
Duplicate of #13042

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