Result of unknown indexing explicitly cast to `any` incorrectly reported as implicit any

<!-- Please try to reproduce the issue with `typescript@next`. It may have already been fixed. --> **TypeScript Version:** typescript@3.4.0-dev.20190311 <!-- Search terms you tried before logging this (so others can find this issue more easily) --> **Search Terms:** "Element implicitly has an 'any' type" " index expression is not of type" We are on the same page that an unknown/untyped indexing operation results in an `any` result. However, it seems that silence the error the object being indexed must be cast to `any`, it is insufficient to cast the result of the indexing itself to `any`. **Code** ```ts declare let foo: HTMLElement; let a = (<any>foo.attributes)["bar"].value; let x = foo.attributes["bar"].value; let y = (<any>foo.attributes["bar"]).value; let z = (foo.attributes["bar"] as any).value; ``` compiled with `tsc --strict ./test.ts` **Expected behavior:** * No error on `let a = ...` because type warnings on any operation on an explicitly `any` type (including indexing) are let through. * An error is thrown on `let x = ...` because the element type resulting from the lookup is of unknown type. * No error on `let y = ...`, not because the type is known but because I'm explicitly casting the `<any>` result to `any`. * No error on `let z = ...`, not because the type is known but because I'm explicitly casting the `<any>` result to `any`. **Actual behavior:** ``` test.ts:3:24 - error TS7015: Element implicitly has an 'any' type because index expression is not of type 'number'. 3 let x = foo.attributes["bar"].value; ~~~~~ test.ts:4:30 - error TS7015: Element implicitly has an 'any' type because index expression is not of type 'number'. 4 let y = (<any>foo.attributes["bar"]).value; ~~~~~ test.ts:5:25 - error TS7015: Element implicitly has an 'any' type because index expression is not of type 'number'. 5 let z = (foo.attributes["bar"] as any).value; ~~~~~ ``` I argue that both `(<an…