SerialDescriptor serialName is not respected

[rcaceiro]

Describe the bug
I have the necessity of build a custom KSerializer, when I try to use your builders I cannot specify the serial name, like the sample below:

override val descriptor: SerialDescriptor = mapSerialDescriptor(
            keyDescriptor = ,
            valueDescriptor = ,
        )

When I try the snippet below the serial name is ignored also:

               private val mSerializer = MapSerializer(
            keySerializer = Scope.serializer(),
            valueSerializer = SetSerializer(elementSerializer = UuidSerializer),
        )
        override val descriptor: SerialDescriptor = SerialDescriptor("custom_name", this.mSerializer.descriptor)

Expected behavior
Or I can pass in the serial name in mapSerialDescriptor and similars, or I can override the serial name with SerialDescriptor

I didn't update yet to 1.8.0 because I am using Ktor 3.0.3 and Ktor uses Kotlinx serialization 1.7.3 and when I tried to update it throws an exception.

Environment

• Kotlin version: 2.1.0
• Library version: 1.7.3
• Kotlin platforms: JVM
• Gradle version: 8.11.1
• Other relevant context JVM 21

[pdvrieze]

@rcaceiro Creating custom list/map serializers does not work well. The reason is that some formats on decoding actually have to go in to the serializer type to access the "append"/update functionality. Obviously this special casing is not supported for custom serializers.