Handle shadow dom

[gs-smuthyam]

I'm submitting a ... (check one with "x")

[x] bug report => Search github for a similar issue or PR before submitting
[ ] feature request
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Current behavior

Expected behavior

ngxDroppable should work with ViewEncapsulation.ShadowDom

Reproduction of the problem

The problem is explained at this thread bevacqua/dragula#418
And a PR is provided at bevacqua/dragula#470

Now since swimlane/dragula is a forked repo and is dependent to this library, need to get the changes to the downstream dependency and make a release here

What is the motivation / use case for changing the behavior?

Using ShadowDom

• Browser: [all | Chrome XX | Firefox XX | IE XX | Safari XX | Mobile Chrome XX | Android X.X Web Browser | iOS XX Safari | iOS XX UIWebView | iOS XX WKWebView ]

all

• Language: [all | TypeScript X.X | ES6/7 | ES5]
  typescript

[gs-smuthyam]

I have picked up the changes into a local branch of https://github.com/swimlane/dragula. However, there is no option to either create a ticket there or push a PR for review. Hence created this ticket here, I'm sure this would be the use case for everyone who starts using Angular Elements as web components