[RFC] Smarter blueprint placer

State now: placer logic is generally dumb, the only reason it works for most of common blueprints is that it builds from bottom to top.

Potential upgrade:
a) iterate the structure unlimited times (unlike 4 block placement stages now)
b) every iteration place such blocks that BlockState#canSurvive(...) in target world, requires special attention for falling blocks (again...)

Solves:
Blocks requiring support without actually checking for support existence (but falling. blocks..) - dripstones, hanging chains
Removes the relatively new block solidness issue out of placer logic (we still need it elsewhere tho)

Doesn't solve:
Pistons and other blocks which may change size or anyhow change local context

Issues:

1. need proper optimizations to fast skip blockPoses that are done already (without world blockstate check? skip fully built layers/rows?)
2. moving redstone blocks (pistons only?) may actually become even worse - solution: special placement handler for powered pistons (mby do additional stage after blocks before entities to check that all redstone blocks incl. actuators are in requested state within one tick)

No source files or tests are named. Start by locating the placer logic and its current four block-placement stages, then inspect how BlockState#canSurvive(...) and falling blocks are handled. Done would require an agreed implementation for repeated placement, optimization, and redstone behavior, plus tests covering the listed cases.