Fix isForgeBlock for runtime deobfuscation

The isForgeBlock check in Block is used to process block place
events appropriately. Was detecting non-vanilla blocks by the
class name length, since obfuscated names are up to 3 characters.
When running in a deobfuscated environment, repackaged srgnames
are used instead - so check for net.minecraft.block as well.
Update to Forge 7.7.1.611