Reland "[ms] [llvm-ml] Improve data support, adding names and complex initializers."

This reverts commit 9fe769a9, and re-lands commit c2e272f8.

Summary: Add support for ?, DUP, and string initializers, as well as MASM syntax for named data locations.

This version avoids the use of a C++17-only feature, if-statements with initializer.

Reviewers: rnk, thakis

Reviewed By: thakis

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D73226