Changes

[489530] Introduced callback mechanism for content transformation.

- Introduced ITransformableContentPart which supports transforming its
contents.
- Enhanced transform policies (AbstractTransformPolicy,
FXTransformPolicy, and FXTransformConnectionPolicy) to chain a content
transform operation within commit, delegating to
ITransformableContentPart (newly introduced).
- Enhanced resize policies (AbstractResizePolicy [extracted],
FXResizePolicy, FXResizeConnectionPolicy) to chain a content operation
within commit, delegating to IResizableContentPart (newly introduced).
- Enhanced bend policies (AbstractBendPolicy [extracted],
FXBendConnectionPolicy) to chain a content operation within commit,
delegating to IBendableContentPart (newly introduced).
- Refactored zest and logo example to no longer use own transform,
resize, and bend policies.