E.g. when there's a type mismatch on the return value of a function. To
fix this, we have to return the expected type as the type of the block
when there's a mismatch. That meant some IDE code that expected
otherwise had to be adapted, in particular the "add return type" assist.
For the "wrap in Ok/Some" quickfix, this sadly means it usually can't be applied
in all branches of an if expression at the same time anymore, because
there's a type mismatch for each branch that has the wrong type.
* Keep codegen adjacent to the relevant crates.
* Remove codgen deps from xtask, speeding-up from-source installation.
This regresses the release process a bit, as it now needs to run the
tests (and, by extension, compile the code).
