Annotation: Support for get/set rich media attributes on text

[jamie-lemon]

Adobe supply this kind of widget in their UI to style annotation text:

However we are unable to read/write to these rich media objects.

[jamie-lemon]

@ccxvii I think the "text alignment" value that is often required is the text alignment set from this kind of rich media.

If I try getQuadding() with the current API on annotation text which has its text alignment changed this way it always returns 0.

[ccxvii]

We support rendering rich media styled text in mupdf core, BUT ONLY IF it is built to include the HTML engine.

1. We do not build the HTML engine for WASM, as this adds a lot of bloat to the binary.

2. The rich style property (RS) is essentially a string of CSS property syntax, which is applied to the rich content (RC) which is a subset of HTML syntax. In theory any changes to the RS and RC should also be reflected into the basic non-rich style properties that we already support. This is not an easy task, because to do so we'd need to parse, generate, and EDIT both CSS and HTML content using the proposed functions.

Parsing we can currently do with the HTML engine, but only enough to get us rendered content. Editing the HTML and CSS is far out of scope for our HTML layout engine.

I suggest we close this as WONTFIX.