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

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

Reviewers: rnk, thakis

Reviewed By: thakis

Subscribers: merge_guards_bot, hiraditya, llvm-commits

Tags: #llvm

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