## Description 

The rules deciding on how to merge user package files between freshly
computed and cached data were incorrect. Luckily (or not actually) they
were not fatally incorrect and while the initial merge (when files were
actually modified) would not succeed, the subsequent one (where no files
were modified - resulting for example from inlay hint request) would,
and ultimately the correct data would be generated.

The problem was spotted in the debug build where debug assertions would
fail on the initial merge (though all would return to normal after
`move-analyzer` restart upon the subsequent request).

I fixed the code and also made it a bit more verbose but also easier to
follow the merge logic

## Test plan 

Verified that assertions are no longer failing in the debug build on
code that was previously triggering them