Use the Shadow DOM for components, isolated styles and templates

### Is your feature request related to a problem? Please describe.
This is not a solution to a problem, but a request to change the architecture of the generated razor DOM elements. At a high level there seems to be a very high degree of correlation in the architectural concepts being provided by Blazor and the Shadow DOM, so why fight it.

### Describe the solution you'd like
Have the Razor components actually generate templates, uses slots and define themselves as shadow DOM elements using javascript classes extending HTMLElement. This would then allow css encapsulation too. Of cause you could start out by defining a class BlazorComponent: HTMLElement.

### Additional context
Nope - I suspect you get the idea.
Might also help the work on allowing interaction with other javascript frameworks. #32352.