Fix GeometryGroup.Children.Clear() leaking shared child geometries - #36232

🔹 [All failing tests from maui-pr]

❌ Microsoft.Maui.IntegrationTests.AndroidTemplateTests.RunOnAndroid(id: "maui-blazor", framework: "net9.0", config: "Debug", trimMode: null) [Details] [1.17% failure rate]

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Failing Configuration

• Integration Tests - mac_runandroid_tests_1

Exception Message

System.ArgumentNullException : Value cannot be null. (Parameter 'format')

CallStack

   at System.ArgumentNullException.Throw(String paramName)
   at System.String.FormatHelper(IFormatProvider provider, String format, ReadOnlySpan`1 args)
   at Microsoft.Build.Logging.StructuredLogger.BuildEventArgsReader.FormatResourceStringIgnoreCodeAndKeyword(String resource, String[] arguments) in C:\MSBuildStructuredLog\src\StructuredLogger\BinaryLogger\BuildEventArgsReader.Viewer.cs:line 198
   at Microsoft.Build.Logging.StructuredLogger.BuildEventArgsReader.GetPropertyReassignmentMessage(String propertyName, String newValue, String previousValue, String location) in C:\MSBuildStructuredLog\src\StructuredLogger\BinaryLogger\BuildEventArgsReader.Viewer.cs:line 72
   at Microsoft.Build.Logging.StructuredLogger.BuildEventArgsReader.ReadPropertyReassignmentEventArgs() in C:\MSBuildStructuredLog\src\StructuredLogger\BinaryLogger\BuildEventArgsReader.cs:line 1266
   at Microsoft.Build.Logging.StructuredLogger.BuildEventArgsReader.ReadBuildEventArgs(BinaryLogRecordKind recordKind) in C:\MSBuildStructuredLog\src\StructuredLogger\BinaryLogger\BuildEventArgsReader.cs:line 319
   at Microsoft.Build.Logging.StructuredLogger.BuildEventArgsReader.Read() in C:\MSBuildStructuredLog\src\StructuredLogger\BinaryLogger\BuildEventArgsReader.cs:line 236
   at Microsoft.Build.Logging.StructuredLogger.BinLogReader.ReadRecordsFromDecompressedStream(Stream decompressedStream)+MoveNext() in C:\MSBuildStructuredLog\src\StructuredLogger\BinaryLogger\BinLogReader.cs:line 350
   at Microsoft.Maui.IntegrationTests.BuildWarningsUtilities.OutputBuildErrorsFromBinLog(String binLogFilePath, Int32 maxErrors, ITestOutputHelper output) in /_/src/TestUtils/src/Microsoft.Maui.IntegrationTests/Utilities/BuildWarningsUtilities.cs:line 46
   at Microsoft.Maui.IntegrationTests.DotnetInternal.Build(String projectFile, String config, String target, String framework, IEnumerable`1 properties, String binlogPath, Boolean msbuildWarningsAsErrors, String runtimeIdentifier, String[] warningsToIgnore, ITestOutputHelper output) in /_/src/TestUtils/src/Microsoft.Maui.IntegrationTests/Utilities/DotnetInternal.cs:line 87
   at Microsoft.Maui.IntegrationTests.AndroidTemplateTests.RunOnAndroid(String id, String framework, String config, String trimMode) in /_/src/TestUtils/src/Microsoft.Maui.IntegrationTests/AndroidTemplateTests.cs:line 113
   at InvokeStub_AndroidTemplateTests.RunOnAndroid(Object, Span`1)
   at System.Reflection.MethodBaseInvoker.InvokeWithFewArgs(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)