Draft: Dump tc and rn ASTs in GHCi with the dump flags

Don't ignore -ddump-tc-ast and -ddump-rn-ast in GHCi. Fixes #17830 (closed).

Note that GHCi dumps stuff with these flags on startup as a result of the generated code to call disableBuffering and flushAll etc.

-ddump-rn flag is removed: it was used in only one place in GHCi. We now dump renamed AST instead.