Implemented a workaround to allow customized rendering of an annotation view.

Annotation views are typically created by TextView when rendering text with
annotations. We want to use annotations for certain inline nodes (such
as formulas), which do not behave like other annotations collecting plain text
and other annotation elements. These annotations apply a complete custom
rendering, e.g., rendering of a formula or an image.
Support image previews for formulas.
Introduced inline-formula as annotation type.