[NFC] Fix potential for use-after-free in DumpModuleInfoAction

Since each `DumpModuleInfoAction` can now contain a pointer to a
`raw_ostream`, saving there a poiter that owned by a local `unique_ptr`
may cause use-after-free. Clarify ownership and save a `shared_ptr`
inside of `DumpModuleInfoAction` instead.
Found by static analyzer.

Reviewed By: tahonermann, aaron.ballman

Differential Revision: https://reviews.llvm.org/D146412