JSInterop improvements

[javiercn]

Right now we just throw an exception when JSInterop gets called within prerendering. We want to provide a better experience for that. There are a few ideas:

• Add Try**** extension methods to JSInterop that will not throw.
• Add some way to figure out whether we are prerendering or not.
• Provide a directive to indicate that a given component can't be prerendered and put a placeholder instead.

[DNF-SaS]

Please also check why await JsRuntime.InvokeAsync() awaits forever when used in Component.OnInitAsync() - it's a real show-stopper if an application needs data from JS for initialization.
See here: #8274

[SQL-MisterMagoo]

While we wait for an official solution, I have provided a nuget package to expose the PreRendering status
https://www.nuget.org/packages/PreRenderComponent/
It just uses a CascadingValue to share "IsPreRendering" with your components/pages.

[SteveSandersonMS]

I'm going to close this in favour of #8786, because there is now more detail over there.