Use bipod when shooting from prone

[ildifa]

Summary

Features "Use bipod when shooting from prone"

Purpose of change

Automatically use the bipod mounted on a gun by shooting from the prone position.

Describe the solution

Added a condition in the code which checks if the terrain is suitable to use the bipod.
Now it checks if the terrain is suitable OR if the player is prone.

Describe alternatives you've considered

Testing

Additional context

[Joshua-Chin]

Going prone doesn't take any time. If we're going to add non-movement related benefits (like bipod usage), we should consider adding a move cost. Tactically, it would force players to choose between a more stable firing position, and a faster initial shot.

[ildifa]

Adding a movecost to going prone (and maybe a higher cost to get back up from prone?) certainly makes sense, but I think it's outside the extent of my ability with C++.
From a purely gameplay perspective, maybe it's not a big deal, as if enemies are close you don't want to be prone anyways. It's possible that players would micro-manage walk->prone->shoot->walk, but it seems quite tedious... I wouldn't do it, at least!

[Joshua-Chin]

My comment isn't intended to block this pull request. It's more of an idea for a subsequent change.