Analyzers to secure [DependsOnClasses] attribute

[olstakh]

This pull request introduces a new analyzer, AttributeUsageDependsOnClassesAnalyzer, to the codebase. The analyzer enforces correct usage of the [DependsOnClasses] attribute by ensuring that dependency types are properly associated with test collections. It reports diagnostics when a dependency already belongs to a collection or when a dependency is not part of any named collection in certain scenarios. The pull request also adds corresponding diagnostic descriptors, updates the analyzer release notes, and provides comprehensive tests for the new analyzer.

Analyzer implementation:

• Added a new analyzer AttributeUsageDependsOnClassesAnalyzer that reports:
  • When a dependency in [DependsOnClasses] already belongs to a collection (via [Collection] or [CollectionDefinition]), suggesting to use [DependsOnCollections] instead.
  • When a dependency is a plain class not part of a named collection and the assembly uses CollectionBehavior.CollectionPerAssembly, suggesting to add [DependsOnClasses(Name = "...")] to the dependency.

Diagnostic descriptors and documentation:

• Added new diagnostic descriptors XIT0013 and XIT0014 to AttributeUsageDescriptors for the analyzer's warnings.
• Documented the new diagnostics in AnalyzerReleases.Unshipped.md.

Testing:

• Added a comprehensive test suite in AttributeUsageDependsOnClassesAnalyzerTests covering all relevant scenarios for the new analyzer, including both positive and negative cases.