Protect -{...}- variant constructs in images.

Protect -{...}- variant constructs in images.

A protected version of explode is factored out as
`StringUtils::delimiterExplode`, since it will be used in follow-up
patches in this series.  The `delimiterExplode` implementation creates
an intermediate array of the exploded results, which is reasonable as
the number of image options is small; but since an Iterator is
returned the implementation can be upgraded in the future (at the cost
of additional complexity) to avoid this.  The additional code in that
case would be similar to ExplodeIterator.

Bug: T146305
Change-Id: I1327685e9e8c07ef476dceaa6f6dae4ba40989ef