Ensure host wiring when scaffolding Blazor Identity

[irfanajaffer]

Fixes #2694

Summary

This PR updates the Blazor Identity scaffolder to automatically apply the
required host-level integration changes when Identity is scaffolded into a
Blazor Web App.

Previously, Identity pages were generated successfully, but the application
was not fully configured to support them, resulting in runtime failures when
navigating to Identity endpoints.

Problem

The Identity scaffolder generated the Account components but did not apply
the additional host wiring required for those components to function in a
Blazor Web App.

As a result:

• Identity pages could be generated successfully.
• Required authentication services were not fully configured.
• Identity routes were not properly integrated.
• Navigating to Identity pages could result in runtime failures.

Changes

Program.cs

Added the required Identity-related application configuration:

• Added AddCascadingAuthenticationState()
• Added required Identity service registrations
• Added support for additional Identity assemblies
• Added MapAdditionalIdentityEndpoints()

App.razor

Updated the generated configuration to support Identity pages that require
non-interactive routing.

Additional Identity Integration

Integrated the host-level changes directly into the scaffolding workflow so
that newly scaffolded applications are configured automatically without
requiring manual updates.

Integration Tests

This PR adds/updates integration tests to verify that host wiring and
generated files are created as expected. Key test expectations include:

• The generated Program.cs contains the required Identity service
  registrations.
• MapAdditionalIdentityEndpoints() is present in the generated host file.
• IdentityRedirectManager, IdentityUserAccessor, and the authentication
  state provider are registered.
• The generated App.razor contains the expected non-interactive routing
  configuration for Identity pages.
• ApplicationUser.cs, the requested DbContext, and Identity account pages
  are created.
• The generated project builds successfully after scaffolding.

The .NET 8 coverage is provided by
BlazorIdentityNet8IntegrationTests.Scaffold_BlazorIdentity_Net8_CliInvocation.
The test now performs these checks unconditionally instead of passing when
the scaffolder produces no Identity files.

Validation

Validated by:

1. Creating Blazor Web App projects without Identity.
2. Running the Identity scaffolder.
3. Verifying the generated host configuration files and App.razor.
4. Verifying the expected Identity files are created.
5. Building the generated project after scaffolding.
6. Running the updated integration tests for .NET 8, .NET 9, and .NET 10.

Compatibility

• No public API changes.
• No breaking changes.
• Changes only affect the generated output of the Blazor Identity
  scaffolder.
• The host-wiring changes support .NET 8, .NET 9, and .NET 10 Blazor Web
  Apps.

.NET 8 compatibility note

.NET 8 Blazor Identity scaffolding already has dedicated templates and a
code-modification configuration in this repository. This PR extends the new
host wiring to that configuration and fixes the .NET 8 template selection so
the expected Identity files are generated.

.NET 8 does not provide HttpContext.AcceptsInteractiveRouting() or
ExcludeFromInteractiveRouting. Its generated App.razor therefore uses a
framework-compatible path check to disable interactive rendering for
/Account routes while retaining interactive server rendering elsewhere.

This behavior is validated by the .NET 8 integration test, which confirms
the generated files, Program.cs registrations and endpoint mapping,
App.razor routing changes, and a successful post-scaffolding build.

Tests

• Integration tests added/updated as described above.
• Unit tests added where applicable to validate the JSON-driven
  CodeModification configs used to insert host wiring.

Screenshot reference

[haileymck]

happy to review after merge conflicts are resolved