Rework of DOM shim (using parse5) to allow for element properties in the future

[briangrider]

Related Issue

First step to resolving issue 170

Summary of Changes

dom-shim.js:

1. Rework DOM shim to use parse5 for serializing children and parsing strings for innerHTML getter and setter
2. Get ShadowDom "closed" mode working
3. Create declarative shadow DOM to mimic the browser functionality when content is appended to a shadowRoot
4. Remove template auto-wrapping functionality from HTMLTemplateElement
5. Add isShadowRoot utility function to check prototype when assessing whether shadowrootmode attribute needs to be added to appended template/content
6. Add deepClone utility function to be used with cloneDeep(deep) functionality (this just returned the actual element before)
7. Add getParse5ElementDefaults utility function to generate empty parse5 elements with much less overhead. At least 2-5x performance gain compared to parsing an empty element in a string (ie. '<template></template>')
8. Add various "TODO" comments for considerations for improvement

wcc.js

1. Simplify renderComponentRoots - no need for getInnerHTML, innerHTML, elementHTML, elementTree, hasLight anymore
2. Remove renderLightDomChildren (passes all tests without)
3. Remove VOID_ELEMENTS (no longer needed by renderLightDomChildren)
4. Simplify renderToString, similar to renderComponentRoots

[thescientist13]

Will try and give this a more thorough testing soon, but just a couple quick observations:

• Since there are no dependency changes, package-lock.json should probably not be changing
• It looks like the tests failed only because of coverage thresholds, and so I'm fine bumping down that as needed (in this case to 85% would be ok)

[briangrider]

Will try and give this a more thorough testing soon, but just a couple quick observations:

• Since there are no dependency changes, package-lock.json should probably not be changing

Ah, my bad. I must have had it accidentally checked on Sourcetree, just reset the branch and pushed just the relevant files

• It looks like the tests failed only because of coverage thresholds, and so I'm fine bumping down that as needed (in this case to 85% would be ok)

Yes, I believe on my initial commit I was at around 91+% on function coverage but it looks like it dipped to 89.28% with some of the additional changes. Yes, if we can temporarily drop the threshold to 85% that would be great