PERF: Flip filter use increment in scanline direction

Improved performance of the FlipImageFilter, by using the
ScanlineIterator for output, and pulling out logic to only occour on a
per scanline basis, reducing per-pixel operation to just a increament
of the index.

Change-Id: I4daa24910cab27a8d52694f54065f8e646337f9b
PERF: Additional FlipImageFilter performance by using input iterator

These combined patches achieve 4-10X improvement over the original
version.

This patch adds an scanline input iterator, computation of the input
region, and separate scanline loops for forward scanline copy and
flipped scanline copy, thereby having a tight inter loop with no
branching.

Change-Id: I1fc04f237bcdd6ffd386642d2e415556c9111d0f
Merge topic 'FlipImageFilterPerformance'

7fa309f PERF: Additional FlipImageFilter performance by using input iterator
c921511 PERF: Flip filter use increment in scanline direction