Fix unrecognized JSpecify nullable annotation locations

[vlsi]

Why

NullAway’s new JSpecifyUnrecognizedAnnotationLocation checker found five @Nullable annotations in locations that JSpecify does not recognize. Those annotations do not express the intended nullness to JSpecify-aware tools.

What

Move wildcard annotations onto their bounds, where JSpecify recognizes them, and remove annotations from a cast and a local-variable root type where the enclosing declarations already express or infer the nullable result.

How to verify

• Built all compileJava tasks with the NullAway snapshot from Add a check for nullness annotations in locations JSpecify does not recognize uber/NullAway#1787 and JSpecifyUnrecognizedAnnotationLocation configured at ERROR severity.
• ./gradlew :core:spring-boot:test --tests org.springframework.boot.context.properties.PropertyMapperTests
• ./gradlew :module:spring-boot-jpa:test --tests org.springframework.boot.jpa.EntityManagerFactoryBuilderTests
• ./gradlew :module:spring-boot-webflux:test --tests org.springframework.boot.webflux.actuate.endpoint.web.AbstractWebFluxEndpointHandlerMappingTests

[vlsi]

Note: for backward compatibility reasons, the checker will be under "suggestion" severity, so if you like to have those as warnings or errors, you would need to adjust JSpecifyUnrecognizedAnnotationLocation checker to ERROR severity in your build scripts.

Note: Spring Framework passes the new checker just fine, no changes required.

[wilkinsona]

The changes to EntityManagerFactoryBuilder have been applied in c38c15b as part of merging this forwards into 4.1.x.

[wilkinsona]

Thanks very much, @vlsi.