* Allow mods to set threshold at which shield stops taking damage
FSO logic dictates that shields collisions and any related sound or visuals related to shields are skipped if the shields are under 10%. This is rather unintuitive especially for mods, so this PR creates a game setting value that allows mods to set this value.
Also, this PR fixes a bug where the HUD shield gauge would try and incorporate this feature but did not do it correctly. Specifically, the gauge skips shield segment rendering if the raw shield strength was 0.1 not the percent. Incorrectly using the raw value results in HUD shields being rendered (albeit faintly) even if the damage was skipping the shield and directly damaging the hull. In other words, if the shield segment was 8%, the shield segment would show faintly even the shield is skipping damage.
Tested and works as expected. Also happy to discuss or answer any questions!
* update local variable name for clarity
* rename `ship_quadrant_shield_strength`
* cleanup with updated get percent function
* more cleanup
* wording and safety tuning
* use correct default number
There is a rather large design flaw in FreeSpace debriefings... debriefing SEXPs can refer to in-mission ship data, while all ships (and all objects) are deleted as soon as the mission completes. Specifically, `obj_delete()` is called which sets all objects to `OBJ_NONE` and marks them as freed, although the data still exists in the various arrays. This is the use-after-free problem, but applied to the in-game object system, rather than memory accessed by pointers.
It's probably best to defer fixes to an as-needed basis. As for hitpoint SEXPs, this change updates them to use the object and ship references from the ship registry, since the ship registry is not cleared by the time the debriefing is loaded. (Using `objp->instance` and `shipp->objnum` at this point would be problematic.) Since subsystems are also cleared at this point, this also updates the warning messages in those functions.
Fixes an Assert seen in debug mode in Inferno.
wookieejedi