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/Step4/MathFunctions/MathFunctions.cxx

@@ -1,19 +1,38 @@
-#include "MathFunctions.h"
+// TODO5: Include <cmath>
 
-#include <cmath>
+#include <format>
+#include <iostream>
 
-#ifdef USE_MYMATH
-#  include "mysqrt.h"
-#endif
+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 << std::format("Computing sqrt of {} to be {}\n", x, result);
+  }
+  return result;
+}
+}
 
 namespace mathfunctions {
 double sqrt(double x)
 {
-// which square root function should we use?
-#ifdef USE_MYMATH
-  return detail::mysqrt(x);
-#else
-  return std::sqrt(x);
-#endif
+  // TODO6: Check if TUTORIAL_USE_STD_SQRT is defined, if so use std::sqrt
+  //        instead of mysqrt
+
+  return mysqrt(x);
 }
 }