[NavMesh Pathfinding] Smoothen the path

[D8H]

Description

• A feature request on this feature: NavMesh pathfinding behavior #2856
• The user should be able to choose to make object speed continuous on the path (not instantly change at each way-point).

Functional solution

• Add a property to smooth the path.
• Allow to constraint how much the smooth path can derive from the original path.

Technical solution

• Bezier curves can be used.
• I didn't think of a solution to find the smooth path but some engines already allow it so the solution must be out there.