[clang-tidy] Use cxxStdInitializerListExpr in modernize-use-emplace

Summary: Use the cxxStdInitializerListExp matcher from ASTMatchers.h instead of a local one.

Reviewers: aaron.ballman, alexfh, Prazek

Reviewed By: aaron.ballman

Subscribers: xazax.hun, cfe-commits

Tags: #clang-tools-extra

Differential Revision: https://reviews.llvm.org/D32923

llvm-svn: 302317