Personally I find most of them to be pretty self explanatory.
Also their location is contextual to the type of action.
So actions related to layers are along the top of the layer panel
Actions associated with overall composition settings are along the bottom of the comp panel.
Project actions the project panel & tools along the top (The tools are really self explanatory ones)
I also know for a fact it would take longer to refer to a "legend" than it would to hover over two or three icons.
Also in hovering over a couple of "wrong" icons you "accidentally" get to learn what those icons are .
So you're not really wasting your time....you're learning. Just another way to look at things.
Ya know, 100 ways NOT to make a light bulb type of thing.
However if you feel a legend would be a better way to go you submit a feature request here
Feature Request/Bug Report Form
Yet another way to look at things is to create a legend yourself...maybe using Photoshop or illustrator.
Make it pretty. Have a few laminated and sell them on Amazon for $5 a pop.
By the time you're done you'll know what every icons means and have a handy dandy reference and maybe you'll earn a few monies here and there.
I should also mention there are already number of very slick "quick reference" sheets available on Amazon that people have made. I own two of them.
Maybe you can find what you're looking for there for 4 or 5 $
https://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias%3Daps&field-keywords=adobe+quic k+reference