Refine multipart converter registration in HttpMessageConverters #35203
Description
As of #33894, HttpMessageConverters auto-detects converters and use custom-provided ones to configure a collection of converters for the client or the server. Right now the multipart converter is only configured if core converters (JSON, XML...) are configured/detected. We do not reuse the base converters (resource, string, byte array) for the multipart converter as it applies different encoding defaults (ISO for the main ones, UTF-8 for multipart).
We should then refine the configuration to not only include the multipart converter when core converters are present, but also if any other converter was configured.