refactor(ui): expose PageService pages

This allows switching between pages and modifying stuff from outside of
that page. Used by Entity Review page's SwitchToEntityEditor method to
switch to the Entity Editor and set its filters.

src/Lumper.UI/Services/PageService.cs

@@ -40,7 +40,7 @@ public sealed class PageService : ReactiveObject
     // Collection of all available pages.
     // For performance, ViewModels are only constructed when the pages are accessed.
     // When a new BSP is loaded, any inactive ephemeral viewmodels are discarded.
-    private readonly Dictionary<Page, ILazyPage<ViewModel>> _pageVms = new()
+    public Dictionary<Page, ILazyPage<ViewModel>> Pages { get; } =
         new()
         {
             { Page.EntityEditor, new LazyPage<EntityEditorViewModel>(true) },
@@ -68,7 +68,7 @@ private PageService() =>
             .ObserveOn(RxApp.MainThreadScheduler)
             .Subscribe(_ =>
             {
-                foreach ((Page page, ILazyPage<ViewModel> pageVm) in _pageVms)
+                foreach ((Page page, ILazyPage<ViewModel> pageVm) in Pages)
                 {
                     // When active BSP file changes (incl. closing), reset any page that is
                     //  - loaded
@@ -91,7 +91,7 @@ public void ViewPage(Page page)
         if (page == ActivePage)
             return;
 
-        if (!_pageVms.TryGetValue(page, out ILazyPage<ViewModel>? pageVm))
+        if (!Pages.TryGetValue(page, out ILazyPage<ViewModel>? pageVm))
             throw new ArgumentException($"Bad page name {page}");
 
         PreviousPage = ActivePage;
@@ -111,7 +111,7 @@ public void ViewPage(Page page)
 
     // This wrapper interface + class is required because we need a covariant type for Get(),
     // so that e.g. LazyPage<VtfBrowserViewModel> is assignable to LazyPage<ViewModel>.
-    private interface ILazyPage<out T>
+    public interface ILazyPage<out T>
     {
         public bool Ephemeral { get; }