[AST] Migrate away from PointerUnion::{is,get} (NFC)#117469

kazutakahirata merged 1 commit intollvm:mainllvm/llvm-project:mainfrom

kazutakahirata:cleanup_001_PointerUnion_ASTkazutakahirata/llvm-project:cleanup_001_PointerUnion_ASTCopy head branch name to clipboard