Issue: SPR-15540

Issue: SPR-15540

Issue: SPR-15540

This commit introduces 2 new @Nullable and @NonNullApi
annotations that leverage JSR 305 (dormant but available via
Findbugs jsr305 dependency and already used by libraries
like OkHttp) meta-annotations to specify explicitly
null-safety of Spring Framework parameters and return values.

In order to avoid adding too much annotations, the
default is set at package level with @NonNullApi and
@Nullable annotations are added when needed at parameter or
return value level. These annotations are intended to be used
on Spring Framework itself but also by other Spring projects.

@Nullable annotations have been introduced based on Javadoc
and search of patterns like "return null;". It is expected that
nullability of Spring Framework API will be polished with
complementary commits.

In practice, this will make the whole Spring Framework API
null-safe for Kotlin projects (when KT-10942 will be fixed)
since Kotlin will be able to leverage these annotations to
know if a parameter or a return value is nullable or not. But
this is also useful for Java developers as well since IntelliJ
IDEA, for example, also understands these annotations to
generate warnings when unsafe nullable usages are detected.

Issue: SPR-15540

Closes gh-1327

See gh-1327

Issue: SPR-15196

Issue: SPR-15160

Dropping GenericCollectionTypeResolver in favor of direct ResolvableType usage.

Issue: SPR-15160

Issue: SPR-15072

Issue: SPR-14832

Issue: SPR-15028

Built-in support in MethodParameter and DependencyDescriptor supersedes our separate KotlinUtils helper.

Issue: SPR-14951

Issue: SPR-14883
(cherry picked from commit b42d731f)

Issue: SPR-14737

Issue: SPR-7549

(cherry picked from commit a4a71a89)

PersistenceAnnotationBeanPostProcessor obtains default EntityManagerFactory via getBean(Class) algorithm

Issue: SPR-7549

Issue: SPR-13188

Issue: SPR-14478

Issue: SPR-14432

Issue: SPR-14432

Issue: SPR-13188

Issue: SPR-14430

Issue: SPR-14400

Closes gh-1039

Issue: SPR-14140

Issue: SPR-13440

Issue: SPR-13987

Issue: SPR-13968

Issue: SPR-5839

Issue: SPR-13956

Issue: SPR-13625