[clang-format][NFC] Allow getLLVMStyle() to take a language

Summary:
getLLVMStyle() sets the default style, but doesn't take the language as a parameter, so can't set default parameters when they differ from C++. This change adds LanguageKind as an input to getLLVMStyle so that we can start doing that.

See D55964 as a motivation for this, where we want Tablegen to be formatted differently than C++.

Reviewers: djasper, krasimir, MyDeveloperDay

Reviewed By: MyDeveloperDay

Subscribers: jdoerfert, MyDeveloperDay, kristina, cfe-commits, arphaman

Tags: #clang

Differential Revision: https://reviews.llvm.org/D56943

llvm-svn: 355123