[clang] [NFC][Clang][Sema] Apply Rule of Three to various classes (PR #174516)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman approved this pull request.

The changes LGTM as far as they go, but we don't have any coding standard requirement for a rule of three (five, zero, etc) and these changes are a noop. If we're going to have tools which enforce a rule like this, should we change the coding standard to mention following the rule?

https://github.com/llvm/llvm-project/pull/174516