Utils: Add Utils::SmallStringView::empty

It is required by many template function because it is used in the STL.

Change-Id: I5a2b9266d0c9d79bdc37cbbc4e7b62fac7a82b8b
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/libs/utils/smallstringview.h

@@ -97,6 +97,12 @@ public:
         return m_size == 0;
     }
 
+    constexpr
+    size_type empty() const noexcept
+    {
+        return m_size == 0;
+    }
+
     constexpr
     const_iterator begin() const noexcept
     {

tests/unit/unittest/smallstring-test.cpp

@@ -1004,6 +1004,12 @@ TEST(SmallString, StringViewIsEmpty)
     ASSERT_TRUE(SmallStringView("").isEmpty());
 }
 
+TEST(SmallString, StringViewEmpty)
+{
+    ASSERT_FALSE(SmallStringView("text").empty());
+    ASSERT_TRUE(SmallStringView("").empty());
+}
+
 TEST(SmallString, HasContent)
 {
     ASSERT_TRUE(SmallString("text").hasContent());