QXmlString: add noexcept to size() and operator QStringView()

size() is obviously noexcept. QStringView ctors have an implied
precondition that the (ptr, n) range passed represent a valid
range. Since this is a member function QXmlString, we can assume that
the class variants hold and m_string itself represents valid (or null)
data, so this operation is also noexcept.

As a drive-by, remove pointless inline keywords.

Change-Id: Ia7637e77005062b6515ceac4b62efaf14a2eb486
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit 792bea9be3760f58de4d1c30fbecab0071fe311e)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/corelib/serialization/qxmlstream.h

@@ -31,8 +31,8 @@ public:
         m_string.swap(other.m_string);
     }
 
-    inline operator QStringView() const { return QStringView(m_string.data(), m_string.size); }
-    inline qsizetype size() const { return m_string.size; }
+    operator QStringView() const noexcept { return QStringView(m_string.data(), m_string.size); }
+    qsizetype size() const noexcept { return m_string.size; }
 };
 
 }