[clang-tidy] Add check 'modernize-return-braced-init-list'

Summary:
Replaces explicit calls to the constructor in a return with a braced
initializer list. This way the return type is not needlessly duplicated in the
return type and the return statement.

```
Foo bar() {
  Baz baz;
  return Foo(baz);
}

// transforms to:

Foo bar() {
  Baz baz;
  return {baz};
}
```

Reviewers: hokein, Prazek, aaron.ballman, alexfh

Reviewed By: Prazek, aaron.ballman, alexfh

Subscribers: malcolm.parsons, mgorny, cfe-commits

Tags: #clang-tools-extra

Differential Revision: https://reviews.llvm.org/D28768

llvm-svn: 295199