core: Use enum class for TestSuite::Type

doc/manual/source/how-to-write-tests.rst

@@ -61,7 +61,7 @@ is called "router" such as here:
 ::
 
   RouterTestSuite::RouterTestSuite()
-    : TestSuite("router", UNIT)
+    : TestSuite("router", Type::UNIT)
 
 Try this command:
 

doc/manual/source/new-modules.rst

@@ -162,7 +162,7 @@ which declares a new unit test named ``new-module``,
 with a single test case consisting of the class ``NewModuleTestCase1``::
 
   NewModuleTestSuite::NewModuleTestSuite()
-    : TestSuite("new-module", UNIT)
+    : TestSuite("new-module", Type::UNIT)
   {
     AddTestCase(new NewModuleTestCase1);
   }

doc/manual/source/test-framework.rst

@@ -761,7 +761,7 @@ as a ''unit'' test with the display name, ``my-test-suite-name``.
   };
 
   MyTestSuite::MyTestSuite()
-    : TestSuite("my-test-suite-name", UNIT)
+    : TestSuite("my-test-suite-name", Type::UNIT)
   {
     AddTestCase(new MyTestCase, TestCase::Duration::QUICK);
   }