Utils: Add more constexpr to SmallString

Change-Id: I480ef040a8d9c5b9edc515c7fd58db2fad42dc86
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/libs/utils/smallstringview.h

@@ -97,11 +97,13 @@ public:
         return m_size == 0;
     }
 
+    constexpr
     const_iterator begin() const noexcept
     {
         return data();
     }
 
+    constexpr
     const_iterator end() const noexcept
     {
         return data() + size();
@@ -140,8 +142,6 @@ public:
         return m_pointer[0] == characterToSearch;
     }
 
-
-
 private:
     const char *m_pointer;
     size_type m_size;