[clang] [clang][Sema] Add -Wswitch-default warning option (PR #73077)

[via cfe-commits]

gendalph wrote:

`
enum class test
{
  err1,
  err2,
  ok
};

int check_err (test v)
{
  switch (v)
    {
      case test::err1:
        return 1;
      case test::err2:
        return 2;
      case test::ok:
        break;
    }
  return 0;
}
`

https://github.com/llvm/llvm-project/pull/73077