Analyzer: Error when Feature Defaults are used to enable other features

[Copilot]

Introduces a Roslyn analyzer and code fix to detect and correct improper feature enablement patterns in NServiceBus features.

Problem:
Using EnableFeature<TFeature>() inside the Defaults method violates NServiceBus best practices. Dependent features should be enabled via the protected Enable<TFeature>() method in the constructor instead.

Changes:

• Added FeatureDefaultsEnableFeatureAnalyzer (NSB0019) to detect EnableFeature<TFeature>() calls within Defaults lambdas
• Added FeatureDefaultsEnableFeatureFixer to automatically move these calls to the constructor using Enable<TFeature>()
• Optimized analyzer performance with syntax-based filtering before semantic model lookups
• Supports FixAll provider for batch corrections across solution

Example:

// Before (triggers NSB0019)
class MyFeature : Feature
{
    public MyFeature()
    {
        Defaults(settings => settings.EnableFeature<DependencyFeature>());
    }
}

// After (code fix applied)
class MyFeature : Feature
{
    public MyFeature()
    {
        Enable<DependencyFeature>();
    }
}

Scoped out:

• Local functions or static methods invoked within Defaults

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