This is in preparation of implementing Reflect.set.

Besides making SetSuperProperty and others return Maybe<bool>, this CL
also fixes some parts of my previous refactoring of SetProperty and
others: It doesn't make sense to take both a language_mode and a
should_throw argument.  A strict language_mode should imply
THROW_ON_ERROR.

R=rossberg, verwaest@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1431443003

Cr-Commit-Position: refs/heads/master@{#31678}