Revert "Remove ipywidgets (#9253)" (#9751)

This reverts commit 43d30fd.

For #3429

src/ipywidgets/.gitignore

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+.DS_Store
+out
+dist
+**/node_modules
+.nyc_output
+npm-debug.log
+bin/**
+obj/**
+tmp/**

src/ipywidgets/.prettierrc.js

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+module.exports = {
+    semi: true,
+    singleQuote: true,
+    printWidth: 180,
+    tabWidth: 4
+};

src/ipywidgets/.vscode/settings.json

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+// Place your settings in this file to overwrite default and user settings.
+{
+    "files.exclude": {
+        "out": true,
+        "**/*.pyc": true,
+        ".nyc_output": true,
+        "obj": true,
+        "bin": true,
+        "**/__pycache__": true,
+        "**/node_modules": true,
+        ".vscode test": false,
+        ".vscode-test": false,
+        "**/.mypy_cache/**": true,
+        "**/.ropeproject/**": true
+    },
+    "search.exclude": {
+        "out": true,
+        "**/node_modules": true,
+        "coverage": true,
+        "languageServer*/**": true,
+        ".vscode-test": true,
+        ".vscode test": true
+    },
+    "[python]": {
+        "editor.formatOnSave": true
+    },
+    "[typescript]": {
+        "editor.formatOnSave": true
+    },
+    "typescript.preferences.quoteStyle": "single",
+    "javascript.preferences.quoteStyle": "single",
+    "typescriptHero.imports.stringQuoteStyle": "'",
+    "cucumberautocomplete.skipDocStringsFormat": true,
+    "[javascript]": {
+        "editor.formatOnSave": true
+    },
+    "editor.codeActionsOnSave": {
+        "source.fixAll": true,
+        "source.fixAll.tslint": true
+    }
+}

src/ipywidgets/README.md

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+# This folder is based off the the sample `web3` from https://github.com/jupyter-widgets/ipywidgets/blob/master/examples/web3
+
+* We have built a custom solution based on `web3` sample to host ipywidgets outside of `Jupyter Notebook`.
+
+# Solution for IPywidgets
+
+* IPywidgets traditionally use [requirejs](https://requirejs.org).
+    * `traditionally` as there seems to be some ongoing work to use `commonjs2`, though unsure how this will work with 3rd party widgets.
+* Using 3rd party widgets require:
+    * [requirejs](https://requirejs.org) to be available in the current browser context (i.e. `window`)
+    * Base `IPywidgets` to be defined using `define` in [requirejs](https://requirejs.org).
+* Rather than bundling using `amd` or `umd` its easier to just import everything using `commonjs2`, then export for `requirejs` using `define` by hand.
+    * `define('xyz', () => 'a')` is a simple way of declaring a named `xyz` module with the value `a` (using `requirejs`).
+    * This is generally done using tools, however we'll hand craft this as it works better and easier.
+    * `amd` is not what we want, as out `react ui` doesn't use `amd`.
+    * `umd` is does not work as we have multiple `entry points` in `webpack`.
+    * Heres' the solution `define('@jupyter-widgets/controls', () => widgets);`