Consider defn name metadata for internal processing

[ikappaki]

HI,

can you please consider patch to enable defn to process name metadata alongside map-attr?. It partly addresses #1178 by allowing defasync to effectively pass meta keys such as :decorators for consideration in defn.

While the actual code change is small, it introduces :decorators tests for defn and defasync, which were previously missing. These tests will help lay the groundwork for the next part: supporting the :decorators meta key for fn.

I've also made a minor adjustement to the defn docstring to make it more obvious that the :decorations key is not only defined over attr-map?.

Thanks

[ikappaki]

This code change turned out to be unnecessary after moving :decorators support to anonymous fn, so I will close it and migrate the tests to the later PR.