feat: add ToProperty, ObservableAsPropertyHelper and [ObservableAsProperty]

[glennawatson]

Summary

Adds ToProperty, which backs a read-only property with the latest value of an observable. The generator writes the code that raises the property's change notification, so each new value allocates nothing and no types are added to the consumer's assembly.

• ObservableAsPropertyHelper<T> holds the latest value and raises the notification for each new one, in order, on the producing thread or a given scheduler. It supports deferred subscription, an initial value or factory, ThrownExceptions, and Default for a property that never changes.
• ToProperty overloads take the property as a selector or a constant name, with an initial value or factory, deferred subscription, a scheduler, and an out parameter for the helper.
• The generator raises through a raise method the type exposes, or adds one small accessor to a partial type that invokes its own event.
• [ObservableAsProperty] on a partial get-only property generates the property body and its helper field.
• ToPropertyUnsafe is the reflection fallback for a call the generator cannot read, such as a name held in a variable. It carries trimming and dynamic-code annotations.
• New analyzer diagnostics: RXUIBIND012 when no notification can be raised, RXUIBIND013 when the property is not named directly, and RXUIBIND014 (error) when a positional string initial value is ambiguous below C# 13.
• Pre-C# 10 file-and-line dispatch now matches Windows paths and chained calls split across lines, for every binding API.
• The benchmarks are configured entirely by the configs each host passes, add a .NET Framework 4.6.2 job on Windows, and cover the new APIs.
• The examples gain a runnable page for every new API and platform verifiers for .NET Framework, .NET 8 to 11, WPF, WinForms and MAUI. The System.Reactive examples are replaced by a README on using the System.Reactive package.

Why

Projects using this generator could not add another source generator to back properties with observables, so they had no way to do it with bindings. Running the new verifiers on .NET Framework on Windows also showed that pre-C# 10 dispatch never matched a Windows path or a multi-line chained call, so those calls threw at run time.

Breaking changes

None.

How this was verified

Tests cover the helper, the generator, the analyzers and the reflection fallback. The platform verifiers ran on Linux and on a Windows machine, for .NET Framework 4.6.2 through .NET 11, WPF, WinForms and MAUI. Apple platforms could not be run here.

Notes for the reviewer

• Start with ObservableAsPropertyHelper.cs, then the ToProperty extractor and code generator. The subtle parts are the helper's gate and serialized delivery, and the dispatch rules for string names and OverloadResolutionPriority.
• RuntimePropertyRaiser suppresses SES1406 on its two lookups that must reach non-public members; this was agreed as the one allowed use.
• Mechanical and safe to skim: the generated ToProperty and ToPropertyUnsafe stub files, the PublicAPI baselines, the verified snapshots, and the removal of attributes from the benchmark classes.
• The documentation is in the website PR: docs(binding): add the ReactiveUI.Binding documentation section website#999

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 failed

Failed conditions
4.7% Duplication on New Code (required ≤ 3%)
C Reliability Rating on New Code (required ≥ A)

See analysis details on SonarQube Cloud

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[codecov]

Codecov Report

❌ Patch coverage is 90.38290% with 108 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.05%. Comparing base (b842759) to head (1a9845c).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...s/ReactiveUIBindingExtensions.ToProperty.Unsafe.cs	41.25%	47 Missing ⚠️
...nerators/CodeGeneration/ToPropertyCodeGenerator.cs	94.36%	15 Missing ⚠️
...ding.Shared/Bindings/ObservableAsPropertyHelper.cs	92.85%	12 Missing ⚠️
...I.Binding.Shared/Fallback/RuntimePropertyRaiser.cs	90.14%	7 Missing ⚠️
...ng.SourceGenerators/Helpers/ToPropertyExtractor.cs	92.30%	7 Missing ⚠️
...ceGenerators/Plugins/PropertyRaise/RaiseMembers.cs	89.18%	4 Missing ⚠️
...I.Binding.Analyzer/Analyzers/ToPropertyAnalyzer.cs	93.33%	3 Missing ⚠️
...alyzer/Analyzers/ToPropertyInitialValueAnalyzer.cs	92.10%	3 Missing ⚠️
...rs/Plugins/PropertyRaise/PartialTypeRaisePlugin.cs	94.73%	3 Missing ⚠️
...Plugins/PropertyRaise/ReactiveObjectRaisePlugin.cs	92.10%	3 Missing ⚠️
... and 3 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #119      +/-   ##
==========================================
- Coverage   98.05%   97.05%   -1.00%     
==========================================
  Files         349      368      +19     
  Lines       12731    13876    +1145     
  Branches     1539     1774     +235     
==========================================
+ Hits        12483    13468     +985     
- Misses        248      408     +160     

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[github-actions]

This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.