For slab and stairs, block_age processor can make non-stone-type to mossy stone type.

Step to reproduce

Because there are some offset, it's better to execute them in an enough open area.

1.  Create a new Classic Flat world and add this data pack.
2.  These blocks are not processed:

   /place template test:bamboo_mosaic_stairs
   /place template test:waxed_cut_copper_slab
   /place template test:waxed_cut_copper_stairs
   

3.  These blocks are processed:

   /place structure test:bamboo_mosaic_stairs
   /place structure test:waxed_cut_copper_slab
   /place structure test:waxed_cut_copper_stairs
   

Expected result:

Non-stone-type blocks should not be turned into mossy stone brick type blocks.

Observed result:

Non-stone-type blocks can be turned into mossy stone brick type blocks.

Notes:

Related to MC-277770