Web support

[mhawryluk]

Currently running an app using react-native-wgpu on the web doesn't work:

Unable to resolve module (...)/node_modules/react-native/Libraries/ReactNative/PaperUIManager.js: 

None of these files exist:
  * node_modules/react-native/Libraries/Utilities/Platform(.web.ts|.ts|.web.tsx|.tsx|.web.js|.js|.web.jsx|.jsx|.web.json|.json|.web.cjs|.cjs|.web.mjs|.mjs|.web.scss|.scss|.web.sass|.sass|.web.css|.css)
  * node_modules/react-native/Libraries/Utilities/Platform
  17 | const NativeModules = require('../BatchedBridge/NativeModules');
  18 | const defineLazyObjectProperty = require('../Utilities/defineLazyObjectProperty');
> 19 | const Platform = require('../Utilities/Platform');
     |                           ^
  20 | const UIManagerProperties = require('./UIManagerProperties');
  21 |
  22 | const viewManagerConfigs: {[string]: any | null} = {};

It would be great if the library could handle this and fall back to browser implementation for the web, allowing to create universal apps for mobile and web without doubling the implementation.

[blazejkustra]

Addressed in #273