[clangd] Make -clang-tidy-checks a non-hidden command-line arg
[clangd] Make -clang-tidy-checks a non-hidden command-line arg

Summary:
This looks like a useful user-facing configuration parameter,
which should be discoverable.

Also fix a small typo in the description.

Reviewers: hokein

Reviewed By: hokein

Subscribers: ioeric, MaskRay, jkorous, arphaman, kadircet, cfe-commits

Differential Revision: https://reviews.llvm.org/D57384

git-svn-id: a34e9779ed74578ad5922b3306b3d80a0c825546@352509 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/clang-tools-extra,llvm-mirror/clang-tools-extra,llvm-mirror/clang-tools-extra,llvm-mirror/clang-tools-extra