Tests: Establish root Tests directory, move Userland/Tests there

With the goal of centralizing all tests in the system, this is a
first step to establish a Tests sub-tree. It will contain all of
the unit tests and test harnesses for the various components in the
system.

Tests/LibGfx/BenchmarkGfxPainter.cpp

@@ -0,0 +1,53 @@
+/*
+ * Copyright (c) 2021, Oleg Sikorskiy <olegsik@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibTest/TestCase.h>
+
+#include <LibGfx/Bitmap.h>
+#include <LibGfx/Painter.h>
+#include <stdio.h>
+
+BENCHMARK_CASE(diagonal_lines)
+{
+    const int run_count = 50;
+    const int bitmap_size = 2000;
+
+    auto bitmap = Gfx::Bitmap::create(Gfx::BitmapFormat::BGRx8888, { bitmap_size, bitmap_size });
+    Gfx::Painter painter(*bitmap);
+
+    for (int run = 0; run < run_count; run++) {
+        for (int i = 0; i < bitmap_size; i++) {
+            painter.draw_line({ 0, 0 }, { i, bitmap_size - 1 }, Color::Blue);
+            painter.draw_line({ 0, 0 }, { bitmap_size - 1, i }, Color::Blue);
+        }
+    }
+}
+
+BENCHMARK_CASE(fill)
+{
+    const int run_count = 1000;
+    const int bitmap_size = 2000;
+
+    auto bitmap = Gfx::Bitmap::create(Gfx::BitmapFormat::BGRx8888, { bitmap_size, bitmap_size });
+    Gfx::Painter painter(*bitmap);
+
+    for (int run = 0; run < run_count; run++) {
+        painter.fill_rect(bitmap->rect(), Color::Blue);
+    }
+}
+
+BENCHMARK_CASE(fill_with_gradient)
+{
+    const int run_count = 50;
+    const int bitmap_size = 2000;
+
+    auto bitmap = Gfx::Bitmap::create(Gfx::BitmapFormat::BGRx8888, { bitmap_size, bitmap_size });
+    Gfx::Painter painter(*bitmap);
+
+    for (int run = 0; run < run_count; run++) {
+        painter.fill_rect_with_gradient(bitmap->rect(), Color::Blue, Color::Red);
+    }
+}