isMounted method is incompatible with Shadow DOM

[e111077]

Description

The method for calculating isMounted doesn't seem to work in shadow DOM, because document.contains() will return false for anything inside of shadow DOM. Consider using Node.isConnected.

Reproduction

link to the svelte example written in Lit

steps:

• add or remove a chip
• observe that the sibling elements after do not animate but flash into position

debugging steps:

• open dev tools
• find console log of autoAnimate
• click on function to open source
• add debugger to the mutation sibling lines
• add a child
• observe mutation previous sibling

[justin-schroeder]

Thanks!

[e111077]

I've pinned down the issue. I've worked on a fix (just add || el.isConnected to the line defining isMounted), but I'm having trouble running the tests to verify I haven't broken anything else.