SpringBoot Property placeholders aren't resolved when configuration property binding creates a Map from a property value using a converter

Change Summary

• Add call to placeholder resolver to ensure property placeholders are resolved for the MapperBinder similar to Binder.java

Issue

• https://github.com/spring-projects/spring-boot/issues/39471

Comment From: scottfrederick

Thanks again @wanger26. I've merged your changes along with a small commit to address formatting.