Feat: A Star Search, Type: AI/ML (TheAlgorithms#1468)

* updating DIRECTORY.md

* Feat: A* Search Algorithm, Type: AI/ML

* Type changes

* Code reformatting.

* Code reformatting-2

* Code refactoring-3.

* Code refactoring-3.

* Code refactoring-4.

* Code refactoring-4.

* Code refactoring-5.

* updating DIRECTORY.md

* Minor changes

* clang-format and clang-tidy fixes for edf593f

* Minor changes-2

* Enhanced AyStarSearch class documentation.

* Adding Closed List for faster A* search.

* Type checks

* Type checks-2

* Comments

* Update machine_learning/a_star_search.cpp

Co-authored-by: David Leal <halfpacho@gmail.com>

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
Co-authored-by: David Leal <halfpacho@gmail.com>

Author: 3 people

DIRECTORY.md

@@ -129,6 +129,7 @@
   * [Gram Schmidt](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/linear_algebra/gram_schmidt.cpp)
 
 ## Machine Learning
+  * [A Star Search](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/machine_learning/a_star_search.cpp)
   * [Adaline Learning](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/machine_learning/adaline_learning.cpp)
   * [Kohonen Som Topology](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/machine_learning/kohonen_som_topology.cpp)
   * [Kohonen Som Trace](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/machine_learning/kohonen_som_trace.cpp)