Add Semigroup/Monoid instances to ST monad

Fixes #14107.

Signed-off-by: Philipp Middendorf <middendorf@plapadoo.de>

Reviewers: austin, hvr, bgamari, RyanGlScott

Reviewed By: bgamari

Subscribers: RyanGlScott, rwbarton, thomie

GHC Trac Issues: #14107

Differential Revision: https://phabricator.haskell.org/D3845