Move physics-state strafehud/physics hud code to ../common_physics.qc

Move physics-state strafehud/physics hud code to ../common_physics.qc

The physics hud and strafehud require similar calculations/variables (e.g. vel,
onslick, speed, immobile, onground, jumpheld (& keys), swimming, alive_player).
Moved all associated code to client/hud/common_physics.qc which runs before the
HUDs are drawn. This prevents duplicate code.
Consequently, includes for these huds could be cleaned up.
Updated strafehud and physics hud code accordingly.
Added GeomLerp to common/physics/player.qh for strafehud.