docs: examples for the remaining public API, including Apple platforms

[glennawatson]

Summary

Every public ReactiveUI member now has a documentation example or a reviewed reason why app code never calls it, including the Apple platforms.

• Core examples. Activation through IActivatableViewModel.Activator, and an IObserver witness subscribed straight to a ReactiveCommand and through ReactiveCommandBase.
• Platform examples. New coverage for AndroidX (the IReactiveObject surface on views, ReactiveActivity results, USB permission requests, the fragment WireUpControls overload), MAUI and WinUI hosts and converters, WinForms panel and table set-method converters, WPF host properties, every TransitioningContentControl transition, the explicit-view WhenActivated overloads, and Blend behaviour properties.
• New Pages/platform-apple project. An iOS and macOS library app covering the view controllers, views, hosts, suspension, and the UIKit table and collection sources, cells and section information. The iOS and macOS workloads exist only on Windows and macOS, so on Linux the project compiles a one-line placeholder.
• Extending IViewFor. A view-location example that bridges a third-party base class to IViewFor with its own activation fetcher.
• ReactiveUI.Binding 8.5.0. Picks up the fix for the generated BindCommand on AppKit NSButton targets, so the macOS example binds its button with BindCommand.
• SourceLink is off for example projects. Examples are never packed, and SourceLink warned when an example built from a copy of the repository without .git. Libraries are unchanged.

Why

A fresh audit of the public surface after the recent Binding, source generator and routing changes found members with no example.

• The handbook pages on reactiveui/website quote these examples verbatim; the matching page changes are in reactiveui/website (linked below).

Breaking changes

None.

• Only example projects and the example build settings change.

How this was verified

Every console page's // Output: blocks match a real run; the platform apps were run on their platforms.

• WPF, WinForms, Blend and WinUI ran on a Windows machine, and their printed output matches the blocks and the pages. Android ran on an emulator, and every quoted log line appears in the real log. The Apple project was built for iOS and macOS on Windows. It has not run on a simulator.

Notes for the reviewer

Start with Pages/platform-apple (new) and src/examples/Directory.Build.props; the rest adds methods to existing page projects.

• src/Directory.Build.props gains one condition: the SourceLink package is skipped when EnableSourceLink is false, which only the examples set.
• The examples include the fix: honour ViewContract in WinUI ViewModelViewHost and add ReactiveWindowController #4527 fixes: the WinUI ViewModelViewHost examples switch views by contract, and the macOS window uses ReactiveWindowController with WhenActivated.
• Companion website PRs: docs(reactiveui): document the remaining public API and add the Apple platform page website#1000 (merged) and docs(reactiveui): WinUI view contracts and ReactiveWindowController website#1001 (the fix: honour ViewContract in WinUI ViewModelViewHost and add ReactiveWindowController #4527 follow-up).

Checklist

• I have read the Contribute guide
• The PR title follows Conventional Commits
• Tests cover this change, or the summary says why they do not
• New or changed public API has XML documentation

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.69%. Comparing base (8dcabad) to head (827ae23).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4526   +/-   ##
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  Coverage   93.69%   93.69%           
=======================================
  Files         175      175           
  Lines        6231     6231           
  Branches      743      743           
=======================================
  Hits         5838     5838           
  Misses        392      392           
  Partials        1        1           

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