Poplar leaves use the wrong transparent-pixel fill when See-Through Leaves is disabled

When 'See-Through Leaves' is disabled, the transparent pixels of poplar leaves are incorrectly filled using the manhattan algorithm, preventing them from displaying the same darker colour as other leaves.

Steps to reproduce:

1. Start Minecraft Java Edition 26.3-snapshot-3;

2. Set ‘See-Through Leaves' to Off;

3. Place red, orange, or yellow poplar leaves next to another type of leaves;

4. Compare the colours used to fill the transparent parts.

the three poplar leaf textures use the manhattan algorithm instead of the single dark-colour fill used by other regular leaves because they do not have corresponding .png.mcmeta files.