Summary
Snow layers can be "waterlogged" by doing /setblock or /fill inside water.

Steps to Reproduce:

1. Stand in a water source block.
2. /setblock ~ ~ ~ snow_layer (any height will do)

You can also repeat the above with /fill.
Observed Results:
A snow layer will be placed in the water, making it "waterlogged".
Additionally,

• The snow layer block can be made taller by placing more snow layers on it, without affecting its "waterlogged" status.
• A "full" snow layer block placed in this manner (either setblock or adding more layers) can continue to have water flowing out.

Expected Results:
The water should disappear and the snow layer should be placed (and washed away if there are adjacent water blocks that can do so).