Updates our js transpiler code to use Babel 7.11.6

List of changes in this commit:

- Updates plugins, babel plugins all have a new version which doesn't contain -es2015- anymore
- Drops (transform-es2015-classes)[https://babeljs.io/docs/en/babel-plugin-transform-classes] this plugin shouldn't be needed now that we don't support IE
- Drops check-es2015-constants, checking constants is now part of babel and the check-constants plugin is deprecated. As a result the behavior slightly changed, and is now wrapping every const call in a readOnlyError function which would throw if assigned a new value. This explains the modified spec.
- Adds (proposal-optional-chaining)[https://babeljs.io/docs/en/babel-plugin-proposal-optional-chaining]

```javascript
const obj = {
  foo: {
    bar: {
      baz: 42,
    },
  },
};

const baz = obj?.foo?.bar?.baz; // 42
```

- Adds (proposal-json-strings)[https://babeljs.io/docs/en/babel-plugin-proposal-json-strings]

```javascript
// IN
const ex = "before
after";
//                ^ There's a U+2028 char between 'before' and 'after'

// OUT
const ex = "before\u2028after";
//                ^ There's a U+2028 char between 'before' and 'after'
```

- Adds (proposal-nullish-coalescing-operator)[https://babeljs.io/docs/en/babel-plugin-proposal-nullish-coalescing-operator]

```javascript
var object = {};
var foo = object.foo ?? "default"; // default
```

- Adds (proposal-logical-assignment-operators)[https://babeljs.io/docs/en/babel-plugin-proposal-logical-assignment-operators]

```javascript
let a;
let b = 2;
a ||= b; // 2
```

- Adds (proposal-numeric-separator)[https://babeljs.io/docs/en/babel-plugin-proposal-numeric-separator]

```javascript
let budget = 1_000_000_000_000;
console.log(budget === 10 ** 12); // true
```

- Adds proposal-object-rest-spread https://babeljs.io/docs/en/babel-plugin-proposal-object-rest-spread

```javascript
let { x, y, ...z } = { x: 1, y: 2, a: 3, b: 4 };
console.log(x); // 1
console.log(y); // 2
console.log(z); // { a: 3, b: 4 }
```

- Adds proposal-optional-catch-binding https://babeljs.io/docs/en/babel-plugin-proposal-optional-catch-binding

```javascript
try {

} catch {

} finally {
  // ensures finally is available in every browsers
}
```

- Adds improved regex support for firefox through [transform-dotall-regex](https://babeljs.io/docs/en/next/babel-plugin-transform-dotall-regex.html) and [proposal-unicode-property-regex](https://babeljs.io/docs/en/babel-plugin-proposal-unicode-property-regex)

- Adds (for-await...of)[https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for-await...of] support for Edge through [proposal-async-generator-functions](https://babeljs.io/docs/en/babel-plugin-proposal-async-generator-functions)

the failues are due to minor differences in the ouput due to new plugins and updated babel