I'm following the tutorial on the website for making a fluid. I can't find the BlockRenderLayer class that is referenced as the return class of getRenderLayer()

The wiki is outdated but this repo is not where you should ask/report, this is the fabric api repo. You should better ask from discord and tell someone to update the wiki.

It is now gone in 1.15. Do the following:

BlockRenderLayerMap.INSTANCE.putFluid(yourFluid, layer);

ok thanks