Weakpoints (Part 7): Add monster defenses

[Joshua-Chin]

Summary

Features "Let monster defend their weak points"

Purpose of change

Monster should be able to defend their weak points. For example, a zombie bio-operator might raise its hands to protect its eyes, or a turtle might retract it head into its shell. In addition, these defenses may vary based on the type of attack.

Describe the solution

Interface

Add support for the following weakpoint fields

• The coverage_mult field is a constant multiplier on the base coverage.
• The difficulty field acts as a soft gating function on the attacker's skill. It multiplies the coverage by the probability that a sample from a normal distribution, centered on the attacker's skill with standard deviation 2, exceeds the difficulty.

Contributors will be able to specify different values for coverage_mult and difficulty depending on the attack type. The following types of attacks are supported:

• Melee Stab: weapons like spears and polearms
• Melee Cut: weapons like swords and knives
• Melee Bash: weapons like clubs and hammers
• Ranged: projectiles and thrown items

The shorthands all, melee, point, and broad are also support. See MONSTER.md for more information.

Implementation

• Add the weakpoint_difficulty struct to weakpoint.h, and implement the JSON parsing.
• Add the attack_type enum to theweakpoint_attack data struct.
• Delay setting the fields of weakpoint_attack as late as possible. This reduces the level of code duplication. (e.g. setting the source for projectiles, melee attacks, and melee techniques, when it could be set just once.)
• Handle the defensive calculations in weakpoint::hit_chance.

Describe alternatives you've considered

See #51915 for discussion and alternatives.

Testing

Manual testing with weakpoint_mon

Additional context

Closes #51915

[lgtm-com]

This pull request fixes 1 alert when merging d58892b into e379588 - view on LGTM.com

fixed alerts:

• 1 for Declaration hides parameter

[Joshua-Chin]

@I-am-Erk FYI, this PR updates weakpoint_attack.is_melee into the more fine grain enum weakpoint_attack.type.

[I-am-Erk]

Arright looks like I gotta do some refinement of weakpoint JSON now