[doc] Update release notes (#2873)

docs/pages/7_0_0_release_notes.md

@@ -247,6 +247,7 @@ The following previously deprecated rules have been finally removed:
     * [#4080](https://github.com/pmd/pmd/issues/4080): \[ant] Split off Ant integration into a new submodule 
 * core
     * [#2234](https://github.com/pmd/pmd/issues/2234): \[core] Consolidate PMD CLI into a single command
+    * [#2873](https://github.com/pmd/pmd/issues/2873): \[core] Utility classes in pmd 7
     * [#3203](https://github.com/pmd/pmd/issues/3203): \[core] Replace RuleViolationFactory implementations with ViolationDecorator
     * [#3902](https://github.com/pmd/pmd/issues/3902): \[core] Violation decorators
     * [#4035](https://github.com/pmd/pmd/issues/4035): \[core] ConcurrentModificationException in DefaultRuleViolationFactory
@@ -354,6 +355,19 @@ The following previously deprecated rules have been finally removed:
   has been moved into the same package {% jdoc_package ant::ant %}. You'll need to update your taskdef entries in your
   build.xml files with the FQCN {% jdoc !!ant::ant.CPDTask %} if you use it anywhere.
 
+* Utility classes in {% jdoc_package core::util %}, that have previously marked as `@InternalApi` have been finally
+  moved to {% jdoc_package core::internal.util %}. This includes ClasspathClassLoader, FileFinder, FileUtil, and
+  IOUtil.
+
+* The following utility classes in {% jdoc_package core::util %} are now considered public API:
+  * {% jdoc core::util.AssertionUtil %}
+  * {% jdoc core::util.CollectionUtil %}
+  * {% jdoc core::util.ContextedAssertionError %}
+  * {% jdoc core::util.ContextedStackOverflowError %}
+  * {% jdoc core::util.GraphUtil %}
+  * {% jdoc core::util.IteratorUtil %}
+  * {% jdoc core::util.StringUtil %}
+
 #### Metrics framework
 
 The metrics framework has been made simpler and more general.