Make codegen default to jspecify NonNull annotations (#1607)

With JSpecify now a dependency of pkl-config-java, this moves the
non-null annotation to jspecify's.
This makes it simpler for users to do nullness checks, as tooling
already understands JSpecify nullness annotations.

docs/modules/java-binding/pages/codegen.adoc

@@ -198,7 +198,7 @@ For Spring Boot applications, and for users of `pkl-config-java` compiling the g
 .--non-null-annotation
 [%collapsible]
 ====
-Default: `org.pkl.config.java.mapper.NonNull` +
+Default: `org.jspecify.annotations.NonNull` +
 Fully qualified name of the annotation type to use for annotating non-null types. +
 The specified annotation type must be annotated with `@java.lang.annotation.Target(ElementType.TYPE_USE)`
 or the generated code may not compile.

docs/modules/pkl-gradle/pages/index.adoc

@@ -423,7 +423,7 @@ For Spring Boot applications, and for users of `pkl-config-java` compiling the g
 .nonNullAnnotation: Property<String>
 [%collapsible]
 ====
-Default: `"org.pkl.config.java.mapper.NonNull"` +
+Default: `"org.jspecify.annotations.NonNull"` +
 Example: `nonNullAnnotation = "org.project.MyAnnotation"` +
 Fully qualified name of the annotation type to use for annotating non-null types. +
 The specified annotation type must be annotated with `@java.lang.annotation.Target(ElementType.TYPE_USE)`

docs/modules/release-notes/pages/0.32.adoc

@@ -37,6 +37,10 @@ The following APIs have been removed without replacement.
 
 * `org.pkl.config.java.Config#makeConfig` (pr:https://github.com/apple/pkl/pull/1531[])
 
+The following APIs have been deprecated for removal.
+
+* `org.pkl.config.java.mapper.NonNull` (https://github.com/apple/pkl/pull/1607[#1607]).
+
 .XXX
 [%collapsible]
 ====