[Customized] Projectile subject to ground check before firing

[CrimRecya]

This is a feature split from #1261 .
It may have similarities with other parts.

If set SubjectToGround to true ,it will predict will predict the height of the connecting straight line from the bullet's source coordinates to target coordinates. If the predicted height is lower than the ground height of the current predicted position, the firer will also consider targets blocked by such obstacles as out of range and will attempt to reposition themselves.

In rulesmd.ini:

[SOMEPROJECTILE]              ; Projectile
SubjectToGround=false         ; boolean

[github-actions]

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[Coronia]

worked properly in testing
updated the doc to indicate that it can't work for buildings and air, and we're all good