Fix JSX children declaration breaking ItemPicker

The way TypeScript (at least the newest version) does excess property
checks prevents some object literals to be used as JSX element content.
This can, at the very least, break the ItemPicker widget in the
tabris-decorators repo.

Change-Id: Iaf33f4364fb2bd3e3918297c215370a41e3ce558

Author: tbuschto

tools/generate-dts.ts

@@ -20,7 +20,7 @@ type ReadOnlyWidgetKeys<T> = T extends {readonly bounds: any}
   : never;
 type MethodKeysOf<T> = { [K in keyof T]: T[K] extends Function ? K : never }[keyof T];
 // Tabris.js Helper Types
-type JSXDefaultChildren = Flatten<string|{cid?: never}>;
+type JSXDefaultChildren = Flatten<string|{cid?: never} & object>;
 export type Properties<
   T extends {set?: any},
   U = Omit<T, 'set'> // prevent self-reference issues