Extend build height via bundled datapack (Java) and behavior pack (Bedrock) - #976

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The existing --disable-height-limit flag previously only told the elevation
pipeline to skip compression, but generated worlds still cut off terrain at
Y=319 because neither Java nor Bedrock honor extended ranges without the
appropriate world extension.

Java (1.21.4+): installs a datapack into <world>/datapacks/arnis_tall/ with
an overworld dimension_type override (Y=-2032..2031) and registers it in
level.dat's DataPacks.Enabled so it activates on first load.

Bedrock (1.21.40+): bundles a behavior pack with minecraft:dimension_bounds
(Y=-512..512) into the .mcworld archive, plus world_behavior_packs.json to
auto-activate it. Writes the data_driven_biomes experiment flag to level.dat
(and the required experiments_ever_used / saved_with_toggled_experiments
markers) — without these, Bedrock silently falls back to vanilla bounds.

scale_to_minecraft now honors per-format caps instead of hard-coding 2031.
Re-enables the GUI toggle for Bedrock (previously force-disabled) and renames
the label to "Extend build height" across all locales.

Minor unrelated tweaks in the same branch:
- Cliff faces now mix cobbled/plain deepslate per-column (50/50) instead of
  always plain deepslate in the under-fill
- Doubled under-fill depth cap from 32 to 64 blocks to seal deeper cliffs
- Added missing data-localize hook on "Anonymous Crash Reports" toggle +
  translations across all 19 locales

Co-Authored-By: scrdest <[email protected]>

The CLI --spawn-lat/--spawn-lng path hardcoded spawn_y = 150 in both SpawnX/Y/Z
and Player.Pos[1]. In vanilla-height worlds Minecraft's auto-relocation masked
the issue, but with extended build height terrain can peak at Y≈2000 — the
player would spawn deep inside stone and only escape via auto-relocation.

Now `set_spawn_in_level_dat` takes an explicit spawn_y, and main.rs derives it
from `ground.level(relative_spawn) + 3` before ground is moved into the
generation pipeline. For flat worlds (no --terrain), this falls back to
ground_level + 3, which is still better than the previous hardcoded 150.

Bedrock was already terrain-aware via BedrockWriter::write_level_dat, no change.

Also addresses Copilot review comments:
- Tighten register_tall_datapack_in_level_dat doc to match actual behavior
  (we rely on fresh-template precondition, not explicit reordering).
- Explain why network_version / inventory_version stay at 1.21.0 even when
  last_opened_with_version / minimum_compatible_client_version bump to 1.21.40
  for extended Bedrock worlds.