[Java][Spring] Insert Annotations to be TYPE_USE Compatible

[Chrimle]

WIP WIP WIP
Relates to #23206 .

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Summary by cubic

Add a test and sample to ensure Java Spring POJOs use TYPE_USE nullability annotations for schema-mapped types, enabling JSpecify compatibility. The test asserts a.b.c.@Nullable PersonCountValue (via importMapping to org.jspecify.annotations.Nullable) instead of @Nullable a.b.c.PersonCountValue (relates to #23206).

^{Written for commit e05e4a1. Summary will update on new commits.}