TerraBlender placeholder biome generation

[gniftygnome]

There is evidence of TB placeholder biome generation in the wild now (i.e. mods are actually using TB methods which cause the placeholder to be returned as the found biome by TB's primary search, then replaced by the secondary search). Despite the performance implications, we must implement TB's double call to MultiNoiseUtil.SearchTree.TreeNode.getResultingNode().

As it does in TB itself, this will result in slower worldgen when generating chunks where the second search is used. However, it should be in line with TB's own behavior and will not further slow any Biolith code paths.

See also:

• Placeholder biome generating Glitchfiend/TerraBlender#140
• Placeholder biome generation Traverse#107