Sanity-check microlab leech plant spawns

[chaosvolt]

Summary

SUMMARY: Balance "Reduce spawn chance of leech stalks and leech pod clusters in microlab variant so there isn't literally 77 monsters packed in a single map tile"

Purpose of change

I stumbled on another weird case of wacky leech plant spawns, turns out the microlab spawn just pre-generates a giant horde with fixed spawns. Given the player has to reach them in the first place, they should already have plenty enough time in the reality bubble to generate critters and propagate without needing such a massive assist.

Describe the solution

1. Axed the weird (and broken, since it sprinkles random cupboards all over the place) tile-based spawns of leech plants with use of place_monster, toning it down to 5-10 each of leech stalks and leech pod clusters (down from 32 and 44 respectively), plus the fixed spawn of the leech blossom.
2. Misc: Shifted the corpse spawns to a 5% chance on standard floor tiles, since the tile-based spawns they used got axed per above.

Describe alternatives you've considered

Converting the weird janky spawn-in-specific-spots-by-tile nonsense into some place_monster spawns allowing us to set exactly the min and max number we want, along with letting us define an area for them to spawn in instead of this weird tile-based method.

Testing

1. Checked affected file for syntax and lint errors.
2. Load-tested and visited microlabs until I found the leech plant variant, found the results to look tolerable.

Before:

After (spawned in via map editor so I could sift through variants without teleporting to microlabs constantly):

Additional context

[scarf005]

still the glass door on right of the reactors and cabinets are somewhat suspicious but let's worry about them later.