[Blazor] Disable preloading for enhanced navigation

[maraf]

Enhanced navigation presents several challenges for preloading

• DOM merging: Preloading elements may be different between pages which may result in different order, resulting in removing and adding elements, resulting in browser triggering more preload requests than necessary.
• WebAssembly runtime state: When navigating between pages, WebAssembly is not restarting, only for the first page we need a preloading element.

This PR disables generating preloading elements from ResourcePreloader when the HTTP request is for enhanced navigation.
It alsore removes previous attempt to solve the DOM merging problem from #63239

[Copilot]

Pull Request Overview

This PR disables resource preloading for enhanced navigation in Blazor to address issues with DOM merging and unnecessary WebAssembly runtime state initialization. Enhanced navigation doesn't need preloading elements since the WebAssembly runtime persists between page navigations.

• Removes special handling of preload elements during DOM synchronization
• Adds enhanced navigation detection to skip WebAssembly asset preloading
• Changes method visibility to enable reuse across components

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
DomSync.ts	Removes preload element detection and special handling during DOM comparison
SSRRenderModeBoundary.cs	Adds enhanced navigation check to skip WebAssembly asset preloading
EndpointHtmlRenderer.Streaming.cs	Changes IsProgressivelyEnhancedNavigation method from private to internal

[javiercn]

/backport to release/10.0

/cc: @maraf I imagine we want this in 10.0

[github-actions]

Started backporting to release/10.0: https://github.com/dotnet/aspnetcore/actions/runs/17470161322