TypeScript: createDefaultImageryProviderViewModels() and similar methods are missing

First of all, thank you for adding TypeScript support. It's really nice to have the API documentation available in the IDEs. When adapting my code to the [webpack-cesium-example](https://github.com/CesiumGS/cesium-webpack-example), I noticed that `import { createDefaultImageryProviderViewModels } from "cesium";` works, but the method is not included in the definitions file, thus the IDEs (e.g. WebStorm in the screenshot below) give a warning. I use `createDefaultImageryProviderViewModels()` to initially change the base map, as mentioned on [stackoverflow](https://stackoverflow.com/questions/37502099/base-map-selector-does-not-work).

In the bundled Cesium.js file, I saw that several methods (e.g. createMaterialPropertyDescriptor, createUniform) are missing in the TypeScript file, whereas others (e.g. createCommand, createGuid) are present. As I'm new to TypeScript, I cannot tell the reason or even a solution, but it would be helpful, when all exported methods would be included and eventually documented.


Start by comparing the TypeScript definitions file with the bundled Cesium.js exports, focusing on createDefaultImageryProviderViewModels(), createMaterialPropertyDescriptor, and createUniform. Check how existing exports such as createCommand and createGuid are represented, then verify that the missing methods no longer produce IDE warnings.

Written by the indexing model from the issue text.