RN: Cleanup ExtendedError Type

Summary:
Cleans up the `ExtendedError` internal type and moves it into a separate module instead of burying it in `parseErrorStack.js`.

Also, this resolves some unnecessary Flow type suppressions.

Changelog:
[Internal]

Reviewed By: GijsWeterings

Differential Revision: D28470299

fbshipit-source-id: 04093243f06f67f41567270ef9778f01c7549b05

Libraries/Core/Devtools/parseErrorStack.js

@@ -15,16 +15,6 @@ import type {HermesParsedStack} from './parseHermesStack';
 
 const parseHermesStack = require('./parseHermesStack');
 
-// $FlowFixMe[incompatible-exact]
-export type ExtendedError = Error &
-  interface {
-    jsEngine?: string,
-    preventSymbolication?: boolean,
-    componentStack?: string,
-    forceRedbox?: boolean,
-    isComponentError?: boolean,
-  };
-
 function convertHermesStack(stack: HermesParsedStack): Array<StackFrame> {
   const frames = [];
   for (const entry of stack.entries) {