move all tests to top-level tests/ directory

tests/indent/cpp/access.cpp

@@ -0,0 +1,6 @@
+class Foo {
+public:
+    int x;
+private:
+    int y;
+};

tests/indent/cpp/class.cpp

@@ -0,0 +1,7 @@
+class Foo {
+    int x;
+    class Bar {
+        int y;
+    };
+    Bar z;
+};

tests/indent/cpp/stream.cpp

@@ -0,0 +1,7 @@
+#include <iostream>
+
+void foo(int x) {
+    std::cout << x
+        << x + 1
+        << x + 2;
+}