This PR adds support for LevelDB (version 1.20.70) worlds together with various other stuff from Nukkit PM1E (changelog) including but not limited to:

lots of new blocks and items
waterlogging
increased world height
dimension changes
nether and the end generator from Cloudburst
fixes for overworld generator
fixes for lagging and crashing exploits
asynchronous chunk and packet sending
new movement mechanics
new APIs including items and entities
new version of RakNet library
performance improvements

Jenkins downloads: https://ci.opencollab.dev/job/NukkitX/job/Nukkit/job/leveldb/

For server owners:

Lots of new blocks, items and game mechanics were added. Test and update your plugins. Make sure land protection etc. plugins are configured to handle new blocks, items and mechanics.
World height was increased and void was moved below the new world height bottom limit.
Support for MCRegion and legacy LevelDB worlds was removed. New worlds are using LevelDB by default.
Timings were removed, use spark instead
Some commands had changes in their functionality:
- All player args require either full player name or a selector
- Give has a default item count of 1 instead of a stack
Attacking entities now resets sprinting (player.attack-stop-sprint: false to disable)
Convert worlds using 'convert' command in console to enable new features. Multiple worlds can be converted at once but don't play on the server while converting.
To back up a running server with LevelDB worlds safely, use 'save-off hold' -> backup -> 'save-on hold' (Note: This disables unloading of modified chunks which increases memory usage temporarily.)

For plugin developers:

Check your plugins for fixed size arrays of block IDs and data values, use Block.MAX_BLOCK_ID and Block.DATA_BITS
Due to increased block data bits, full block IDs have changed. Recompile plugins which shift block ID by 4 and use Block.DATA_BITS (6). Or better, don't have your plugin depend on full IDs at all!
Notice increased world height (from 0-255 to -64-319, negative y coordinates!)
Block hash values changed due to increased world height
Notice separation of block and item ID for blocks with ID over 255 (itemId = 255 - blockId, negative item block IDs!)
Always use Block.get and Item.get instead of creating new Block and Item instances and do not compare them using 'instanceof'
Prefer Block.isBlockTransparentById(id) instead of Block.transparent[id] (same for solid[], light[], etc.)
Get and set Block methods now have BlockLayer (NORMAL/WATERLOGGED) as optional argument
Timings API was removed
Added API for custom items
Added API for custom entities
Added API for material types and material tags
Added API for persistent containers
Added entity/blockEntity.canSaveToStorage/setSaveToStorage to allow disabling saving of certain entites/block entities
Added level.isSaveOnUnloadEnabled/setSaveOnUnloadEnabled to allow disabling saving of unloaded chunks (remember to also disable auto save)
Added level.setLightUpdatesEnabled to allow disabling block light updates on block placement for better performance when light is not used
Some protected/internal APIs were removed/changed
Use API version 1.1.0 to require latest Nukkit

Contains (at least partially) or should make following pull requests obsolete:

417, #786, #879, #914 , #1819, #1280, #1493, #1511, #1873, #1908, #1967, #2117, #2197

Contains parts of code from other projects: Cloudburst Server, PowerNukkit

Should resolve following issues:

2178, #2160, #2036, #2001, #2000, #1885, #1706, #1605, #1604, #1593, #1573, #1563, #1540, #1482, #1456, #1383, #1378, #1367, #1340, #1324, #1320, #1200, #864, #846, #839, #785, #733, #702, #698, #660, #497, #444, #418, #398, #325, #272, #116

Co-author: @Alemiz112

CloudburstMC / Nukkit

LevelDB support & other updates #2175

417, #786, #879, #914 , #1819, #1280, #1493, #1511, #1873, #1908, #1967, #2117, #2197

2178, #2160, #2036, #2001, #2000, #1885, #1706, #1605, #1604, #1593, #1573, #1563, #1540, #1482, #1456, #1383, #1378, #1367, #1340, #1324, #1320, #1200, #864, #846, #839, #785, #733, #702, #698, #660, #497, #444, #418, #398, #325, #272, #116