Re-implement missing level-sensitive block light hook in ChunkAccess (#9536)

src/main/java/net/minecraftforge/common/extensions/IForgeBlock.java

@@ -87,7 +87,27 @@ public interface IForgeBlock
     /**
      * Get a light value for this block, taking into account the given state and coordinates, normal ranges are between 0 and 15
      *
+     * @param state The state of this block
+     * @param level The level this block is in
+     * @param pos The position of this block in the level, will be {@link BlockPos#ZERO} when the chunk being loaded or
+     *            generated calls this to check whether it contains any light sources
      * @return The light value
+     * @implNote <ul>
+     *     <li>
+     *         If the given state of this block may emit light but requires position context to determine the light
+     *         value, then it must return a non-zero light value if {@code (pos == BlockPos.ZERO)} in order for the
+     *         chunk calling this to be considered as containing light sources.
+     *     </li>
+     *     <li>
+     *         The given {@link BlockGetter} may be a chunk. Block, fluid or block entity accesses outside of its bounds
+     *         will cause issues such as wrapping coordinates returning values from the opposing chunk edge
+     *     </li>
+     *     <li>
+     *         This method may be called on a worker thread and must therefore use
+     *         {@link IForgeBlockGetter#getExistingBlockEntity(BlockPos)} to retrieve the {@link BlockEntity}
+     *         at the given position
+     *     </li>
+     * </ul>
      */
     default int getLightEmission(BlockState state, BlockGetter level, BlockPos pos)
     {