[CodeComplete] Constructor overload candidates report as vector(int) instead of vector<string>(int)
This is shorter, shouldn't be confusing (is consistent with how they're declared),
and avoids messy cases that are printed as myclass<type-param-0-0>(int) in the
case of partial specialization.
Fixes part of https://github.com/clangd/clangd/issues/76
Reviewers: hokein, lh123
Subscribers: ilya-biryukov, kadircet, usaxena95, cfe-commits
Differential Revision: https://reviews.llvm.org/D70307