src/ now contains all source code - in subdirectories, according to the
.cabal component they belong to. This will allow us to put vendored
libraries in the same place - and later split our own code into multiple
components/libraries as well.
Jumping past GHC 9.6, 9.8 and 9.10 immediately, because these versions
do not successfully build the static binary with TemplateHaskell and
iserv-proxy, yet.
Michal wrote the changes to hsie.
Co-authored-by: Michal Kleczek <michal@kleczek.org>