Utils: Introduce flexible constructor for SmallString and SmallStringView

If a class has a data method that returns a char pointer it can be 
used to construct a SmallString and a SmallStringView.

Change-Id: I02dcba50babb3074b58998e5f907799e84361ed7
Reviewed-by: Ivan Donchevskii <ivan.donchevskii@qt.io>

src/libs/utils/smallstring.h

@@ -126,13 +126,17 @@ public:
         : BasicSmallString(BasicSmallString::fromQString(qString))
     {}
 
-    template<typename Type,
+    BasicSmallString(const QByteArray &qByteArray)
-             typename = std::enable_if_t<std::is_same<std::decay_t<Type>, std::string>::value>
+        : BasicSmallString(qByteArray.constData(), qByteArray.size())
-             >
-    BasicSmallString(Type &&string)
-        : BasicSmallString(string.data(), string.size())
     {}
 
+    template<typename String,
+             typename Utils::enable_if_has_char_data_pointer<String> = 0>
+    BasicSmallString(const String &string)
+        : BasicSmallString(string.data(), string.size())
+    {
+    }
+
     template<typename BeginIterator,
              typename EndIterator,
              typename = std::enable_if_t<std::is_same<BeginIterator, EndIterator>::value>

src/libs/utils/smallstringview.h

@@ -34,6 +34,18 @@
 
 namespace Utils {
 
+template <typename String>
+using enable_if_has_char_data_pointer = typename std::enable_if_t<
+                                            std::is_same<
+                                                std::remove_const_t<
+                                                    std::remove_pointer_t<
+                                                        std::result_of_t<
+                                                            decltype(&String::data)(String)
+                                                            >
+                                                        >
+                                                    >, char>::value
+                                            , int>;
+
 class SmallStringView
 {
 public:
@@ -67,7 +79,9 @@ public:
     {
     }
 
-    SmallStringView(const std::string &string) noexcept
+    template<typename String,
+             typename Utils::enable_if_has_char_data_pointer<String> = 0>
+    SmallStringView(const String &string) noexcept
         : m_pointer(string.data()),
           m_size(string.size())
     {