[clang][CodeComplete] Propogate printing policy to FunctionDecl
Summary:
Printing policy was not propogated to functiondecls when creating a
completion string which resulted in canonical template parameters like
`foo<type-parameter-0-0>`. This patch propogates printing policy to those as
well.
Fixes https://github.com/clangd/clangd/issues/76
Reviewers: ilya-biryukov
Subscribers: jkorous, arphaman, usaxena95, cfe-commits
Tags: #clang
Differential Revision: https://reviews.llvm.org/D72715
