[http-client-csharp] ModelReaderWriterContextDefinition does not discover models from method return types or properties introduced by custom code

[haiyuazhang]

For both cases, we need to use custom code to add the ModelReaderWriterBuildable attribute.

case1: Models used only as method return types are not discovered

https://github.com/Azure/azure-sdk-for-net/blob/7c44a7be77e762fe6a5e50d36fefa42eba829db5/sdk/workloadssapvirtualinstance/Azure.ResourceManager.WorkloadsSapVirtualInstance/src/Custom/AzureResourceManagerWorkloadsSapVirtualInstanceContext.cs#L11

case2: Properties introduced by custom code are not discovered

https://github.com/Azure/azure-sdk-for-net/blob/7c44a7be77e762fe6a5e50d36fefa42eba829db5/sdk/oracle/Azure.ResourceManager.OracleDatabase/src/Custom/Models/AzureResourceManagerOracleDatabaseContext.cs#L13

[JoshLove-msft]

@haiyuazhang, for case 1, is this type represented as a ModelProvider in the generated library? We collect all model providers here, but it seems this might be a completely custom type? Or is this a common core type? Can you clarify whether the method that uses this type is found in a ClientProvider?

[JoshLove-msft]

Ended up adjusting the logic to consider methods for all TypeProviders.