Implementing fixes for Unity 2021.3 LTS

[ByteSz]

Addressed main issues brought up so far related to working in Unity 2021.3 and from a fresh download.

Changelog:

• Replaces "GetOrAddComponent" extension calls with base "GetComponent" & "AddComponent" function calls
• Implemented an alternative replacement for "Gizmos.DrawLineList" by using "Gizmos.DrawLine" in existing foreach loop

Closes #2
Closes #3

[HunterProduction]

Here is a little comment on the implementation, suggesting a small improvement to the fixes

[HunterProduction]

There is a problem with index increment in this loop. Calling i++ will already increment the index after the instruction is completed.

// Here i == 0
points[i++] = centerOfMass;
// Here i == 1
points[i++] = otherCenterOfMass;
// Here i == 2
Gizmos.DrawLine(points[i], points[i++]);

Here is the problem. We should link with a line points[0] and point[1], but index is already been incremented so we are probably skipping array elements. The following index management should be more robust.

points[i] = centerOfMass;  
points[i + 1] = otherCenterOfMass; 
Gizmos.DrawLine(points[i], points[i + 1]); 
i += 2;

By the way, I used DrawLineList since it's declared to be a more optimized method to draw multiple lines in a raw, so I think we should keep it for newer versions of Unity, and add this fix as an optional code with a condition at compile time checking for the Unity version:

#if UNITY_2023_1_OR_NEWER
// We can use the version with DrawLineList
#else
// We can use the one with simple DrawLine
#endif