Tutorial: Rewrite using conventions enabled by CMake 3.23

This is a full re-write of the CMake Tutorial for CMake 3.23, both
the functionality it provides, as well as the modern workflows that
developers use when interfacing with CMake.

Issue: #22663, #23086, #23799, #26053, #26105, #26153, #26914

Help/guide/tutorial/Step1/MathFunctions/CMakeLists.txt

@@ -0,0 +1,2 @@
+# TODO12: Move all the MathFunctions target commands to this CMakeLists.txt.
+#         Ensure that all paths are updated to be relative to this new location.

Help/guide/tutorial/Step1/MathFunctions/MathFunctions.cxx

@@ -0,0 +1,31 @@
+#include <iostream>
+
+namespace {
+// a hack square root calculation using simple operations
+double mysqrt(double x)
+{
+  if (x <= 0) {
+    return 0;
+  }
+
+  double result = x;
+
+  // do ten iterations
+  for (int i = 0; i < 10; ++i) {
+    if (result <= 0) {
+      result = 0.1;
+    }
+    double delta = x - (result * result);
+    result = result + 0.5 * delta / result;
+    std::cout << "Computing sqrt of " << x << " to be " << result << std::endl;
+  }
+  return result;
+}
+}
+
+namespace mathfunctions {
+double sqrt(double x)
+{
+  return mysqrt(x);
+}
+}

Help/guide/tutorial/Step1/MathFunctions/MathFunctions.h

@@ -0,0 +1,5 @@
+#pragma once
+
+namespace mathfunctions {
+double sqrt(double x);
+}