Improve plants/plant plugin

[Bumber64]

Rename the plants plugin to plant to match the command, making it easier to find docs.

Add command plant remove to remove plants. (Doesn't work on mature trees yet. Will need to reverse-engineer proper tile removal at a later date.) Add plant list to list shrub and sapling raw IDs, avoiding use of lengthy devel/query command and excluding grasses.

Adds a bunch of options to existing plant create and plant grow. See: docs/plugins/plant.rst. Use proper logic for determining plant watery flag, adding to wet/dry vector.

Minor improvement to regrass to accept numerical raw ID for grass type. regrass --list replaces regrass --plant "". Don't remove mud on regrass (since DF doesn't.)

plants doc tag now encompasses tools that affect grass, to include regrass plugin.

---

• Requires (genericize DataIdentity for container types #4591) to pass vector ref to Lua
• plant uses its own cuboid struct. This can be replaced by a more global one: Cuboid struct/class for df::coord bounds #4595