[clang-tidy][NFC] Update ReleaseNotes to mention some performance changes in checks

Included a note in the release documentation about the improved
performance of certain checks, allowing users who had previously
disabled them due to slowness to reconsider their decision.

clang-tools-extra/docs/ReleaseNotes.rst

@@ -268,6 +268,9 @@ Changes in existing checks
   <clang-tidy/checks/bugprone/incorrect-roundings>` check by adding support for
   other floating point representations in float constant like ``0.5L``.
 
+- Improved the performance of the :doc:`bugprone-reserved-identifier
+  <clang-tidy/checks/bugprone/reserved-identifier>` check through optimizations.
+
 - Deprecated check-local options `HeaderFileExtensions` and `ImplementationFileExtensions`
   in :doc:`bugprone-suspicious-include
   <clang-tidy/checks/bugprone/suspicious-include>` check.
@@ -322,6 +325,9 @@ Changes in existing checks
   <clang-tidy/checks/llvm/header-guard>` check.
   Global options of the same name should be used instead.
 
+- Improved the performance of the :doc:`misc-confusable-identifiers
+  <clang-tidy/checks/misc/confusable-identifiers>` check through optimizations.
+
 - Deprecated check-local options `HeaderFileExtensions`
   in :doc:`misc-definitions-in-headers
   <clang-tidy/checks/misc/definitions-in-headers>` check.
@@ -413,6 +419,9 @@ Changes in existing checks
   string for ``Prefix`` or ``Suffix`` options could result in the style not
   being used.
 
+- Improved the performance of the :doc:`readability-identifier-naming
+  <clang-tidy/checks/readability/identifier-naming>` check through optimizations.
+
 - Fixed a false positive in :doc:`readability-implicit-bool-conversion
   <clang-tidy/checks/readability/implicit-bool-conversion>` check warning would
   be unnecessarily emitted for explicit cast using direct list initialization.