[libc++] Use bounded iterators in std::string_view when the debug mode is enabled

Differential Revision: https://reviews.llvm.org/D142903

NOKEYCHECK=True
GitOrigin-RevId: a845b5b4fb8a0070a6e296c462fd62bb17d74bff
diff --git a/docs/ReleaseNotes.rst b/docs/ReleaseNotes.rst
index 268df3a..8a04afb 100644
--- a/docs/ReleaseNotes.rst
+++ b/docs/ReleaseNotes.rst
@@ -41,6 +41,9 @@
 Improvements and New Features
 -----------------------------
 
+- ``std::string_view`` now provides iterators that check for out-of-bounds accesses when the safe
+  libc++ mode is enabled.
+
 Deprecations and Removals
 -------------------------