Remove downcasts in BlazorWebView

[Eilon]

Instead, put "SendXyz" methods on the IBlazorWebView interface to enable the handlers to raise events on the control. The control has events for users to wire-up, or alternative systems can implement the interface with another event/command pattern if desired.

Motivation:

• The concrete class BlazorWebView is what a MAUI user will program against. As such, it has friendly "events" that they can handle and perform various customizations
• The IBlazorWebView interface is the minimum set of APIs needed for a Handler to interact with a concrete usable type, such as MAUI's built-in BlazorWebView, or perhaps some other variation that could be used in Comet or in some hypothetical future version of Hybrid Blazor Bindings. In such non-MAUI places, using events or even structuring the properties the way they are is not necessarily the best model, so they can choose to implement those features however they want (or even omit some that they don't want to use)
• The handlers must talk only to the interface. This enables others to build their own handlers that talk to the interface and can be used with any concrete implementation. For example, a new Tizen BlazorWebViewHandler would talk to the interface and be 100% usable with the existing BlazorWebView MAUI control.

Related: #5904, #5905

[rmarinho]

I would drop the "Send"

[SteveSandersonMS]

Makes sense and looks good!

As for whether or not to remove the Send name prefixes, I'd be in favour of removing them.

[SteveSandersonMS]

About these names:

SendBlazorWebViewInitializing
SendBlazorWebViewInitialized

Do we need to say it's a BlazorWebView here? Could they be named just WebViewInitializing/WebViewInitialized?

I mean I know it could even go as far as Initializing/Initialized but at that point there's a high risk of clash. Since their purpose is to indicate that the external native webview is initializing/initialized (as opposed to the MAUI control) it seems reasonable to have WebView in the name still.

[Eilon]

Do we need to say it's a BlazorWebView here? Could they be named just WebViewInitializing/WebViewInitialized?

Right now it matches the event names, which I think is valuable. Or are you suggesting renaming the events, too?

I would drop the "Send"

I will try to see if that's possible, but it might not work because the control has concrete events X, Y, and Z, and then also interface implementations for methods named X, Y, and Z. I doubt C# allows that.

[Eilon]

OK, the Send prefix is gone. I guess C# is OK with having the same name on an event and an interface-implemented method!

[Eilon]

BTW I didn't rename the methods/event names to drop BlazorWebView. We should discuss that separately because it's a somewhat unrelated change. I think keeping the method names the same as the event names (or extremely similar) is critical. But I'd be fine if we agreed to rename all of them to some other pattern.