Add a unit test for wxImage::Scale() method.

Check that resizing the test horse image produces the same results in the
future as it does now, by saving the current results in files and verifying
that images resized directly and loaded from these files are the same.

See #15281.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74318 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Add benchmarks for wxImage methods.

Build a GUI version of the benchmark program too and use it to benchmark
wxImage loading methods for now (more will be added later).

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74319 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Add wxImage::Scale() benchmarks.

Measure the time taken to rescale the image to a bigger or smaller size using
normal or high quality.

See #15281.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74320 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Optimize wxImage::Scale() by pre-calculating the values used.

Precompute the values used by various resampling algorithms once instead of
doing it for each pixel. This dramatically speeds them up: more than 3 times
faster in wxImage benchmark with the small images and up to 5 times faster
with larger images.

Closes #15281.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74321 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775