QByteArray: bring end() into idiomatic form

For contiguous containers, end() is always begin() + size(), so use
that instead of data() + size().

Centralizes what it means to be an iterator in just begin() now, which
will simplify a follow-up commit of Thiago's.

Pick-to: 6.5
Change-Id: I53ca1a335910bdea3d46b9496ba39bc1a2d3fd93
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit 9dd19532187bd6a5465e6c98a554d24dad1d06d0)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/corelib/text/qbytearray.h

@@ -429,8 +429,8 @@ public:
     const_iterator begin() const noexcept { return data(); }
     const_iterator cbegin() const noexcept { return begin(); }
     const_iterator constBegin() const noexcept { return begin(); }
-    iterator end() { return data() + size(); }
-    const_iterator end() const noexcept { return data() + size(); }
+    iterator end() { return begin() + size(); }
+    const_iterator end() const noexcept { return begin() + size(); }
     const_iterator cend() const noexcept { return end(); }
     const_iterator constEnd() const noexcept { return end(); }
     reverse_iterator rbegin() { return reverse_iterator(end()); }