Ensure all packages declare package-info.java with null-safety annotations

This commit picks up where the two previous commits left off.

Specifically, this commit:

- Removes the "severity=warning" configuration to ensure that violations
  actually fail the build.
- Fixes regular expressions for suppressions by matching forward
  slashes using `[\\/]` instead of `\/`.
- Moves the configuration for newly introduced checks to locations in
  checkstyle.xml that align with the existing organization of that file.
- Renames the IDs for RegexpSinglelineJava checks from
  javaDocPackageNonNullApiAnnotation/javaDocPackageNonNullFieldsAnnotation
  to packageLevelNonNullApiAnnotation/packageLevelNonNullFieldsAnnotation,
  respectively, since these checks are not related to Javadoc.
- Simplifies the null-safety annotation checks to match against
  imported annotation types, which enforces consistency across
  package-info.java files for the annotation declarations.
- Simplifies the RegEx for JavadocPackage suppressions to only exclude
  packages not under src/main/java (vs src/main) and those in the
  framework-docs module.
- Consistently suppresses all checks for the `asm`, `cglib`, `objenesis`,
  and `javapoet` packages in spring-core.
- Adds explicit suppressions for null-safety annotations for the `lang`
  package in spring-core.
- Adds explicit suppressions for null-safety annotations for the
  `org.aopalliance` package in spring-aop.
- Revises the RegEx for null-safety annotation suppressions to only
  exclude package-info.java files not under src/main/java and
  additionally to exclude package-info.java files in the framework-docs
  module as well as those in the spring-context-indexer,
  spring-instrument, and spring-jcl modules.
- Adds all missing package-info.java files.
- Adds null-safety annotations to package-info.java files where
  appropriate.

Closes gh-30069

spring-aspects/src/main/java/org/springframework/beans/factory/aspectj/package-info.java

@@ -0,0 +1,9 @@
+/**
+ * AspectJ-based dependency injection support.
+ */
+@NonNullApi
+@NonNullFields
+package org.springframework.beans.factory.aspectj;
+
+import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-aspects/src/main/java/org/springframework/cache/aspectj/package-info.java

@@ -0,0 +1,9 @@
+/**
+ * AspectJ-based caching support.
+ */
+@NonNullApi
+@NonNullFields
+package org.springframework.cache.aspectj;
+
+import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-aspects/src/main/java/org/springframework/context/annotation/aspectj/package-info.java

@@ -0,0 +1,11 @@
+/**
+ * AspectJ-based dependency injection support driven by the
+ * {@link org.springframework.beans.factory.annotation.Configurable @Configurable}
+ * annotation.
+ */
+@NonNullApi
+@NonNullFields
+package org.springframework.context.annotation.aspectj;
+
+import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-aspects/src/main/java/org/springframework/scheduling/aspectj/package-info.java

@@ -0,0 +1,9 @@
+/**
+ * AspectJ-based scheduling support.
+ */
+@NonNullApi
+@NonNullFields
+package org.springframework.scheduling.aspectj;
+
+import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-aspects/src/main/java/org/springframework/transaction/aspectj/package-info.java

@@ -0,0 +1,9 @@
+/**
+ * AspectJ-based transaction management support.
+ */
+@NonNullApi
+@NonNullFields
+package org.springframework.transaction.aspectj;
+
+import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;