[NewPM] Use a separate struct for ModuleMemorySanitizerPass

Split MemorySanitizerPass into MemorySanitizerPass (as a function
pass) and ModuleMemorySanitizerPass (as a module pass).
Main reason is to make sure that we have a unique mapping from
ClassName to PassName in the new passmanager framework, making it
possible to correctly identify the passes when dealing with options
such as -print-after and -print-pipeline-passes.

This is a follow-up to D105006 and D105007.