Support DOM Annotation for Blazor Component's source file locatio

[chabiss]

In order to support
Experience 1758042: [Blazor Hybrid] Provide a Live Visual Tree/XAML Live Preview that works better with WebView

1. An object model is needed to allow walking the Blazor Component tree.
   Similar to VisualTreeHelper Class (System.Windows.Media) | Microsoft Learn , Blazor also needs a navigable logical component tree. This allows an injected Agent to traverse and gather data to construct the JSON that is sent to the LVT tree via the VDEP protocol.

2. An event system when the Blazor component tree changes
   Similar to VisualTreeChangeEventArgs Class (System.Windows.Diagnostics) | Microsoft Learn, or MutationObserver - Web APIs | MDN (mozilla.org) on modern Browser, events plays a role in updating the Live Visual Tree when changes are made through Hot Reload.

3. Source Info Annotation
   Information known as Source Information is kept within the Blazor Component Tree to pinpoint the origin of the Blazor Component. During Hit Testing, which is conducted at the DOM level by the WebView, the DOM needs to retains information that aids in identifying the Blazor Web Component. This Source Info is crucial for the Blazor Web Component to locate and navigate to the original Source on the Razor page.

Based on a meeting with the Razor, we can solve 1) and 2) (DOM Mutation) by using 100% the DOM Element Tree to rebuild the Blazor Component Tree assuming that 3) contains the require annotation in the generate HTML.

So the request here is for 3) to have the Razor Compiler to

Generate DOM annotation that give the source location of the razor component. The annotation needs to contain:

1. The source filename (relative path)
2. Line Number
3. Column number of the the start tag
   

Annotation would be contain on the DOM Element similar to

[chsienki]

We'll need to effectively add some Blazor source mappings to the generated HTML so that we can reconstruct the original tree. This shouldn't be too difficult given the current compiler infrastructure, as we already have all the info we need to generate said mappings.

Estimate it's probably 4 days of dev work, plus some coordination with the consuming team to make sure we're providing the correct information.