refactor: avoid repeating the return type from the declaration; use a braced...

refactor: avoid repeating the return type from the declaration; use a braced initializer list instead [modernize-return-braced-init-list]

NB: using the braced-initializer list uncovered an error here:
the float returned by std::floor() can't be implicitly cast to
an int. This is solved by using base::ClampFloor<int>() instead.
std::floor()

Co-authored-by: Charles Kerr <charles@charleskerr.com>