Smooth out npc fear based on player strength

[sparr]

Summary

None

Purpose of change

The effect of player strength on NPC fear is weirdly granular, with a jump from -1 to -3, and different range size for each value.

Describe the solution

Replace the list of conditions with simple arithmetic. High strength effects are mostly unchanged. Low strength effects are changed slightly.

Describe alternatives you've considered

Testing

ran test suite, talked to some NPCs with different characters and didn't see unusual fear responses

Additional context

str  0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20
old -3 -3 -3 -3 -1 -1 +0 +0 +0 +0 +0 +0 +1 +1 +1 +1 +2 +2 +2 +2 +2
new -2 -2 -2 -2 -1 -1 -1 -1 +0 +0 +0 +0 +1 +1 +1 +1 +2 +2 +2 +2 +3