[clang-tidy] Add check: replace string::find(...) == 0 with absl::StartsWith

Patch by Niko Weh!

Reviewers: hokein

Subscribers: klimek, cfe-commits, ioeric, ilya-biryukov, ahedberg

Differential Revision: https://reviews.llvm.org/D43847

llvm-svn: 327111