Memory corruption issure for DenseStringElementsAttr

Summary: There was a memory corruption issue where the lifespan of the ArrayRef<StringRef> would fail. Directly passing the data will avoid the issue.

Reviewers: rriddle

Reviewed By: rriddle

Subscribers: mehdi_amini, jpienaar, shauheen, antiagainst, nicolasvasilache, arpith-jacob, mgester, lucyrfox, liufengdb, Joonsoo, grosul1, frgossen, Kayjukh, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D78850