Make CustomRender more flexible

[hnvn]

Currently, CustomRender returns a Widget, it makes the application can't manipulate the alignment of the WidgetSpan which layout of custom tag (it's required in some cases, for example: align an inline image)

My pull request will modify CustomRender, it will return a dynamic type instead of Widget, so the application can return WidgetSpan instead of Widget. In case of returning WidgetSpan, html_parser will return the customRender directly instead of wrapping it inside a WidgetSpan:

...
typedef CustomRender = dynamic Function(RenderContext context,
    Widget parsedChild, Map<String, String> attributes, dom.Element element);
...

InlineSpan parseTree(RenderContext context, StyledElement tree) {
   ...
   if (customRender?.containsKey(tree.name) ?? false) {
      final render = customRender[tree.name].call(
        newContext,
        ContainerSpan(
          newContext: newContext,
          style: tree.style,
          shrinkWrap: context.parser.shrinkWrap,
          children: tree.children
                  ?.map((tree) => parseTree(newContext, tree))
                  ?.toList() ??
              [],
        ),
        tree.attributes,
        tree.element,
      );
      return render is InlineSpan
          ? render
          : WidgetSpan(
              child: ContainerSpan(
                newContext: newContext,
                style: tree.style,
                shrinkWrap: context.parser.shrinkWrap,
                child: render,
              ),
            );
    }
   ...
}

With this approach, the application can freely style the WidgetSpan of custom tag.

[erickok]

Nice job. Looks good. Can you add any concrete example of a typical use?

[hnvn]

For example, I want to add a small inline image between text content, laTeX image in my case, these images should be aligned with text content in baseline instead of center by default.

[DFelten]

What's the status of this merge request? This would be great.

[erickok]

I checked this and it is working well. Unfortunately it is also coming with a bunch of unrelated changes and it has a merge conflict with #384 , When that latter PR is merged I'd like to add this PR's code too.

[erickok]

I re-implemented this in #498 with just the minimal changes required to allow InlineSpans as customerRender.

[hnvn]

As @erickok 's comment, this PR can be closed now