Add Theta* Path Planner

[Musab1Blaser]

Can we add the Theta* Path Planner. It is used in ROS2 Navigation Stack and its inclusion would make the list of path planners more comprehensive.

[Musab1Blaser]

If a need for this is found. Do tag me, I would love to work on it!

[AtsushiSakai]

PR is welcome

[Musab1Blaser]

Great. I have thought of breaking the task into 2 different stages/PRs:

• Implementing Basic Theta*
• Optimizing with AP Theta* (if deemed relevant)

Both are detailed in this paper: https://cdn.aaai.org/AAAI/2007/AAAI07-187.pdf

Nav2 uses a more advanced variant of Theta* called Lazy Theta* P, however, that may be harder to extract key ideas from, and may also be a bit beyond my current skill level.

If you have any immediate feedback, please do share.
I'll work on this over the week as I get the chance. Excited to contribute!

[Musab1Blaser]

@AtsushiSakai I have submitted a PR with a corresponding PR to the gif repository. The code is highly similar to the A* code so it should also be easy to navigate. Do let me know whatever else I can do to improve the commit. Note that I have implemented Basic Theta* and not AP Theta* for now.