Corrected the alpha interpolation order during blending.
This also corrected the hard mix blending result in the guitar sample.
issue: https://github.com/thorvg/thorvg/issues/2704
The anti-aliased outline color was incorrectly blended
at the multiply option.
The fix can be observed in the example:
'examples/lottie/resourcesguitar.json'
in order to do this, RenderMehthod::blend() method introduced
`bool direct` for figuring out the intermediate composition.
Spec out this incomplete experimental feature,
this is a still promising one, we will reintroduce
this officially after 1.0 release
size: -2kb
issue: https://github.com/thorvg/thorvg/issues/1372
