[Blazor] Custom JS initializers (#34798)

* Users can create an ES6 module with `<packageName>.lib.module.js` and declare a beforeStart and afterStarted function to integrate into the blazor start process.
* In WebAssembly beforeStart receives the BlazorWebAssemblyStartOptions object and any publish extension as part of the method arguments.
* In Server beforeStart receives the CircuitStartOptions object and can configure any necessary details.
* In Desktop beforeStart does not receive any argument for the time being.
* afterStarted receives the Blazor object as argument in all cases.
* Callbacks in beforeStart and afterStarted are not invoked in any defined order and are invoked in parallel.