Use FixedHypot over P_AproxDistance

Not convinced that the small speed benefit from P_AproxDistance is worth the "aproximate"[sic] results it gives. Let's instead try a define to replace it with FixedHypot. In Lua, the function gives a deprecated warning.

Inspired by the hyperwall fix for vanilla, except for everything. From little testing, actively improves waypoint checks, bumping, speed checks, wall collisions, Jawz targetting, Lightning Shield attacks, so on.

The only way I see this as a potential downgrade is A_Look (and related functions) getting slower, which are barely used in Kart.