Fix missing (de)serializer registration after workspace refresh

[Copilot]

When running kiota client generate --refresh, the generated TypeScript client had empty if blocks for serializer/deserializer registration, causing compile errors.

Root cause

BaseApiConsumerConfiguration.UpdateGenerationConfigurationFromBase was clearing the default serializer/deserializer collections:

config.Serializers.Clear();
config.Deserializers.Clear();

Language refiners replace the C# defaults with language-specific ones only when the collection matches the defaults in count and content:

if (modules.Count == initialNames.Count && modules.All(initialNames.Contains))
{
    propertySetter.Invoke(currentMethod, moduleNames);  // never reached
}

After clearing (count = 0), the condition 0 == 4 always fails — no replacement happens, and the generated client emits empty registration blocks.

Fix

• BaseApiConsumerConfiguration.cs — Remove the two Clear() calls. A fresh GenerationConfiguration is always constructed before calling UpdateGenerationConfigurationFromApiClientConfiguration, so the C# defaults are always present and available for language refiners to replace.
• ApiClientConfigurationTests.cs — Update the assertion to verify defaults are preserved (NotEmpty) rather than cleared.

• Fixes Refreshing TypeScript clients in workspace removes (de)serializer registration #7584