Implement EZP-22443: RichText generic template tags

This PR resolves issue https://jira.ez.no/browse/EZP-22443

This implements two things:

1. generic template rendered tags
2. refactoring of embed implementation to use templates

Both are handled through Symfony implementation of RichText `RendererInterface`.

## Generic template tags

Internal format defines `eztemplate` and `eztemplateinline` generic tags.
Example:

```xml
<eztemplate name="blockquote">
  <ezcontent>You need to select nodes in a XML tree in ways that consider complex relationships within the hierarchical structure</ezcontent>
  <ezconfig>
    <ezvalue key="cite">Sal Magnano</ezvalue>
    <ezvalue key="book">XSLT Cookbook</ezvalue>
  </ezconfig>
</eztemplate>
```

Generic template tags can have content (inside `ezcontent` element) and configuration (`ezconfig`) describing arbitrary hash structure, introduced in https://github.com/ezsystems/ezpublish-kernel/pull/758.
Element `ezcontent` content is of mixed type, meaning it does not accept only text, but also other elements, depending if its tag is inline or block level.

Template used for rendering these will be looked up in Renderer, by default in `ezsettings.default.fieldtypes.ezrichtext.tag.<name>` YAML configuration.
`fieldtypes.ezrichtext.tag` part is passed as an argument to the Renderer and is therefore configurable.

In the template used for rendering following variables will be available:

* name (name/identifier of the tag)
* align
* class
* content (from `ezcontent`)
* params (from `ezconfig`)

Automatic transformation for legacy XmlText custom tags to RichText template tags is implemented. This makes possible to use RichText template tags to handle rendering of XmlText custom tags if such conversion is configured.

Default inline and block level templates are implemented, rendering instructions to configure template for the tag in case.

Configuration also defines `configuration` key, for the moment unused. That will be used for tag widget configuration in the editor, retrievable through XHR/REST.

## Embed templates

Previous embed implementation from https://github.com/ezsystems/ezpublish-kernel/pull/758 is refactored to use templates for dispatching subrequests.

Example:

```xml
<div class="{% if align is defined %}align-{{ align }}{% endif %}{% if class is defined %} {{ class }}{% endif %}">
{{
    render(
        controller(
            "ez_content:embedContent",
            {
                "contentId": id,
                "viewType": view,
                "params": params
            }
        )
    )
}}
</div>
```

Template used for rendering embeds will be looked up in Renderer, by default in `ezsettings.default.fieldtypes.ezrichtext.embed.<embedType>` YAML configuration.
`fieldtypes.ezrichtext.embed` part is passed as an argument to the Renderer and is therefore configurable.

In the template used for rendering following variables will be available:

* id (Content or Location id)
* view (viewType)
* align
* class
* params (from `ezconfig`)

Template configuration loaded depends on the resource (Content or Location), block or inline context and if resource is accessible by the user. Default inline and block level templates are implemented, rendering instructions to configure template for the embed in case.

See `default_settings.yml` in Core bundle for more details.

### Possible followups

In Legacy Stack it is possible to configure override for any template. This means that it is possible for example to configure custom inline embed template by ContentType or some other parameter.

Such functionality is not implemented here, but if decided necessary it can be implemented in a followup using matchers.

## TODOs

- [x] componentize ezxml-docbook conversion (fix remaining failure)
- [x] test Renderer
- [x] fix rendering of nested template tags

## Additional

* Minor docblock fixes
* Renamed converter EzLinkToHtml5 to Link