Always ensure player spawn chunk is generated

[dktapps]

Problem description

Currently we only require the player's spawn chunk to be generated if they're a new player trying to find a safe spawn.

We do not do this for general player joins since we don't need a safe spawn for those cases; however, we do currently sync-load the chunk here for reasons I'm not completely clear on:

PocketMine-MP/src/player/Player.php

Lines 345 to 349 in 1c6a4bd

	$xSpawnChunk = $spawnLocation->getFloorX() >> Chunk::COORD_BIT_SIZE;
	$zSpawnChunk = $spawnLocation->getFloorZ() >> Chunk::COORD_BIT_SIZE;
	$world->registerChunkLoader($this->chunkLoader, $xSpawnChunk, $zSpawnChunk, true);
	$world->registerChunkListener($this, $xSpawnChunk, $zSpawnChunk);
	$this->usedChunks[World::chunkHash($xSpawnChunk, $zSpawnChunk)] = UsedChunkStatus::NEEDED;

I believe this was needed in years past because the chunk needed to exist in order to add the player to it. However, this is no longer the case. In particular the chunk may not exist if the terrain isn't generated, but this currently seems to be fine.
(It's probably also needed to avoid redundant chunk reloading, since the spawn chunk would be unloaded after promise fulfillment if this wasn't present.)

This is problematic for a few reasons:

• It stands in the way of implementing async chunk I/O as per Async chunk I/O #6560
• We're pre-registering on the chunk before player data decoding, which we can't properly deal with if there's an error (Invalid player NBT tag types crash the server #4647)

Proposed solution

• Register as a chunk loader after calling the parent constructor, so that data loading throwing exceptions doesn't leave dead chunk loaders stuck on the World
• Consider using orderChunkPopulation() async mechanism for existing players to guarantee that the spawn terrain will be loaded & generated. However I'm not clear if this is actually even necessary anyway.

Alternative solutions or workarounds

No response