remove the following utilities used in unit tests which check for features
that are supported by all supported browsers:
- supportsCustomElements
- supportsWebAnimation
- supportsRegExUnicodeFlag
- supportsTemplateElement
also remove the following utilities which check for features that are
not supported (and aren't going to be) by any of the supported browsers:
- supportsDeprecatedCustomCustomElementsV0
- supportsDeprecatedShadowDomV0
PR Close#47543
When using ViewEncapsulation.ShadowDom, Angular will not remove the child nodes of the DOM node a root Component is bootstrapped into. This enables developers building Angular Elements to use the `<slot>` element to do native content projection.
PR Close#24861
