Liquids should be more well defined

there are inconsistencies with liquids. currently, it is impossible to run the following. 

/execute as @s at @s if block ~ ~-1 ~ flowing_water run say hi

strangely, the f3 screen would have me believe otherwise- as looking at the flowing water would show it as "looking at liquid:flowing_water", with no clear indication of what that means. another example:

/fill ~5 ~ ~5 ~-5 ~5 ~-5 water replace flowing_water

this doesn't work

so, here is my suggestion:

Make liquids completely separate from blocks, and run on their own set of rules.

some examples of the above commands adjusted to work with this system are as follows:

/fill ~5 ~ ~5 ~-5 ~5 ~-5 liquid water replace liquid flowing_water

/execute as @s at @s if liquid ~ ~-1 ~ flowing_water run say hi

in the execute example, players simply need to replace "block" with "liquid" to test for liquid instead of blocks.in the fill example, players use the "liquid" argument to indicate that they are filling using a liquid rather than a block. in this case, a command that replaces liquid water with block dirt in a 10x10 area would look like this: /fill ~5 ~5 ~5 ~-5 ~-5 ~-5 block dirt replace liquid water