docs: add changelog and upgrade_450

Author: kenjis

user_guide_src/source/changelogs/v4.5.0.rst

@@ -33,6 +33,8 @@ Others
 - **Logger:** The :php:func:`log_message()` function and the logger methods in
   ``CodeIgniter\Log\Logger`` now do not return ``bool`` values. The return types
   have been fixed to ``void`` to follow the PSR-3 interface.
+- **Autoloader:** The prefix ``\`` in the fully qualified classname returned by
+  ``FileLocator::findQualifiedNameFromPath()`` has been removed.
 
 Interface Changes
 =================

user_guide_src/source/installation/upgrade_450.rst

@@ -72,6 +72,14 @@ reversed.
         Previous: route1 → route2 → filter1 → filter2
              Now: route2 → route1 → filter2 → filter1
 
+FileLocator::findQualifiedNameFromPath()
+========================================
+
+In previous versions, ``FileLocator::findQualifiedNameFromPath()`` returns Fully
+Qualified Classnames with a leading ``\``. Now the leading ``\`` has been removed.
+
+If you have code that expects a leading ``\``, fix it.
+
 Removed Deprecated Items
 ========================