Remove the ActionCache in V3

For V3, I think it is completely possible to implement the ActionCache in terms of the Asset API. This would allow it to be more flexible and less specialized.

To maintain the performance characteristics as pointed out by @sstriker, we would need to probably add support for inlining of blobs/trees into the responses returned from the Asset API so as to not introduce another hop to the CAS.

Start by locating the existing ActionCache and Asset API definitions and reviewing how their responses handle blobs and trees. Determine the V3 design needed to express ActionCache behavior through the Asset API while preserving performance through inlining; no specific files or tests are named.

Written by the indexing model from the issue text.