-ddump-stg-cg doesn't work in ghci

Summary

-ddump-stg-cg doesn't work in ghci. This happens because we print out STG in doCodeGen. Since bytecode is now using optimized stg, it is probably reasonable to move the printing logic to myCoreToStg.

Steps to reproduce

ghc -ddump-stg-cg --interactive
...<use ghci>...
...<observe that no stg output is printed to stdout>...

Expected behavior

STG is printed out when generating bytecode and using -ddump-stg-cg

Environment

• GHC version used: HEAD