Add Object.assign polyfill or backwards compatibility library for IE support

[Anthropic]

Enhancement

Add Object.assign polyfill or backwards compatibility module for IE support.

This can be either a script for supporting legacy browsers or included by default, that shall depend on the need for any other polyfills to support IE11

Awaiting feedback from @donalmurtagh @ramakrij @shravanmahankali @krptodr :)

Related issues

This is related to #864.

@json-schema-form/angular-schema-form-lead

[donalmurtagh]

I'll test out the latest alpha with this polyfill. It'll likely have to wait until next week though, as I'm on vacation for 2nd half of this week

[krptodr]

I can confirm the polyFill resolves the issue with Internet Explorer 11. The form seems to load properly. However, it appears there is an issue with ngCloaking when rendering the form. This could be related to the polyFill implementation OR Alpha.5

[Anthropic]

@krptodr can you describe what you mean regarding ngCloaking issue, what is happening that shouldn't?

[krptodr]

@Anthropic It seems like the cloaking doesn't work. You can see the {{modelvalues}} while the form is rendering.

[Anthropic]

I assume you are meaning while using ng-cloak or just without but while it loads? I think $ref support making it async has some unintended side effects like that which need to be looked into.