5.6 hotfix for broken projectiles

[perkinslr]

Reasoning

• Projectile Height returned a cached value. Projectile next position relied on projectile height. This lead to projectile height being frozen.
• Deprecating ProjectileCE.Height makes it clear that ProjectileCE.ExactPosition is the sole authority on CE-related projectile positioning. Also it removes a virtual lookup so will have marginally better performance.
• By storing the next "frame" directly into ExactPosition and then pulling a local copy inside Tick, subclasses of ProjectileCE can override how ExactPosition gets updated entirely, without forcing updating ExactPosition into a virtual call in the trivial case.
• Explicitly initializing ExactPosition and LastExactPosition during launch removes a messy and moderately expensive calculation and removes the need for a nullable, which should further help performance.
• Projectiles should use their current rather than initial height for determining where to draw shadows

Testing

Check tests you have performed:

• Compiles without warnings
• Game runs without errors
• (For compatibility patches) ...with and without patched mod loaded
• Playtested a colony (minutes)

[github-actions]

You can download the rebuilt assembly for this PR here: https://combatextended.lp-programming.com/CombatExtended-7723738719.zip