Handle nested block operations in analyzer

Adds support for analyzing nested block operations in 'get' accessors, improving compatibility with code generated by other tooling. The analyzer now correctly identifies return operations within nested blocks.

Author: Sergio0694

src/CommunityToolkit.Mvvm.SourceGenerators/Diagnostics/Analyzers/UseObservablePropertyOnSemiAutoPropertyAnalyzer.cs

@@ -148,7 +148,16 @@ public override void Initialize(AnalysisContext context)
                         // We expect a top-level block operation, that immediately returns an expression
                         if (context.OperationBlocks is not [IBlockOperation { Operations: [IReturnOperation returnOperation] }])
                         {
-                            return;
+                            // Special case for nested blocks (e.g. for code generated by some other tooling)
+                            if (context.OperationBlocks is [IBlockOperation { Operations: [IBlockOperation { Operations: [IReturnOperation nestedReturnOperation] }] }])
+                            {
+                                returnOperation = nestedReturnOperation;
+                            }
+                            else
+                            {
+                                // Invalid 'get' accessor structure, we have to stop here
+                                return;
+                            }
                         }
 
                         // Next, we expect the return to produce a field reference