…rt` in MAUI sample (#4320)

…nd MAUI TFMs in sample projects (#4321)

Addresses all open review comments on #4319. The MAUI sample used
`NavigationPage` while calling `Shell.Current?.DisplayAlert(...)`,
guaranteeing a null reference and silent no-op alerts. The `Cancel`
command in all three sample ViewModels was always enabled, contradicting
its doc comment. The WPF `PasswordChanged` binding used reflection-based
`FromEventPattern`, and the MAUI project targeted `net10.0` instead of
deployable platform TFMs.

## MAUI: Shell navigation
- Added `AppShell.xaml` / `AppShell.xaml.cs`; `App.xaml.cs` now creates
`new AppShell()` instead of `new NavigationPage(new LoginPage())`

## MAUI: Alert handling — no more `async void`
Replaced the `async void` subscribe + `Shell.Current?.DisplayAlert`
pattern with a proper Rx chain using the `ContentPage` instance method:
```csharp
ViewModel.Login
    .SelectMany(success => Observable.FromAsync(() =>
        DisplayAlert(
            success ? "Login Successful" : "Login Failed",
            success ? "Welcome!" : "Invalid credentials.",
            "OK")))
    .Subscribe()
    .DisposeWith(d);
```

## All three ViewModels: `Cancel` respects `Login.IsExecuting`
A `Subject<Unit>` breaks the circular dependency (`Login` needs a cancel
signal; `Cancel` needs `Login.IsExecuting`):
```csharp
var cancelSubject = new Subject<Unit>();

Login = ReactiveCommand.CreateFromObservable(
    () => Observable.Return(Password is "secret")
        .Delay(TimeSpan.FromSeconds(1), scheduler)
        .TakeUntil(cancelSubject),
    canLogin, scheduler);

Cancel = ReactiveCommand.Create(
    () => cancelSubject.OnNext(Unit.Default),
    Login.IsExecuting, scheduler);
```

## WPF: AOT-safe `FromEventPattern`
Swapped the reflection overload for the strongly-typed delegate
overload:
```csharp
Observable.FromEventPattern<RoutedEventHandler, RoutedEventArgs>(
    h => Password.PasswordChanged += h,
    h => Password.PasswordChanged -= h)
```

## MAUI csproj: proper platform TFMs
Replaced `<TargetFramework>net10.0</TargetFramework>` with
platform-specific TFMs (`net10.0-android`;
`net10.0-ios`/`net10.0-maccatalyst` on macOS/Windows;
`net10.0-windows10.0.19041.0` on Windows), added
`<OutputType>Exe</OutputType>`, `SupportedOSPlatformVersion`, and
Windows packaging properties.

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: glennawatson <5834289+glennawatson@users.noreply.github.com>

…ld keyword

- Use Shell.Current.DisplayAlertAsync instead of obsolete DisplayAlert
- Use C# 13 field keyword for auto-properties with RaiseAndSetIfChanged
  across all example ViewModels (Samples, Builder.WpfApp, BlazorServer)
- Remove explicit backing fields where field keyword replaces them
- Add IDisposable to sample LoginViewModels for cancel Subject ownership
- Suppress SA1500/SA1513 for field keyword property initializer syntax

The default CodeQL setup uses build-mode 'none' which results in low
analysis quality for compiled languages (69% call targets, 82% expression
types vs 85% thresholds). Switch to manual build mode with dotnet build
to give CodeQL full compilation context.

Excludes Android and Apple targets since platform SDKs are not available
on the CI runner -- core, WPF, WinForms, WinUI, Blazor, and MAUI (net10.0)
targets provide sufficient coverage for security analysis.

The workflow referenced the deleted integrationtests/ directory.
Samples are now built as part of the main CI build via reactiveui.slnx.

The Android SDK has a Mono.Cecil XARRA7028 bug where
RemoveRegisterAttribute cannot find System.Runtime v10.0.0.0
when building net10.0-android Exe projects on CI Linux runners.

On CI Linux, fall back to net10.0 (library build) so the code
still compiles and is validated. Locally and on CI Windows/macOS,
the full platform TFMs are used including net10.0-android.

…platform TFMs

Workload restore now handles previous SDK feature bands correctly,
so the Android/iOS/Mac platform targets should work on CI.

…tandard platform TFMs"

This reverts commit 083bc10.

- Create BuilderTestExecutorBase and BuilderTestExecutor in Executors/
  for per-test state reset and core services bootstrap
- Set assembly-level executor via [assembly: TestExecutor<BuilderTestExecutor>]
- Remove builder init from assembly hooks in WinForms, Tests, Testing,
  AOT, and Builder test projects (keep ModeDetector only)
- Add [assembly: TestExecutor<WinFormsTestExecutor>] for WinForms tests
- Add [assembly: TestExecutor<AppBuilderTestExecutor>] for Testing tests
- Remove inline ResetBuilderStateForTests/ResetForTesting calls from
  Builder test methods (executor handles reset)
- Add custom RxAppMigrationTestExecutor for tests needing RxCacheSize/
  RxState/RxSuspension reset
- Add WithBlazorExecutor and WithDrawingExecutor for platform-specific
  builder configuration
- Add global usings for Splat.Builder, TUnit.Core.Executors,
  TUnit.Core.Interfaces to Builder.Tests csproj