Support @NestedConfigurationProperty at targets other than field

[snicoll]

@NestedConfigurationProperty can't be set in the getter. If a nested property is deprecated, the field is usually removed (to remap to the new namespace). There should be a way to specify that annotation at getter level

If a nested property is deprecated all its keys should be flagged as deprecated automatically as well.

[pkostrzewa]

I can take a look at this with some guidance.

Are you asking to extend NestedConfigurationProperty's target with ElementType.METHOD?

Additionally, should configuration processor check whether a method annotated with NestedConfigurationProperty is actually a getter?

[regulskimichal]

Also, this could be useful in case of using @ConstructorBinding. Right now, there is no way of telling Spring Boot to create metadata for a POJO injected via constructor.

[wilkinsona]

Closing in favor of #38844.