Fix EZP-23059: RichText embeds and template tags are missing semantic configuration

This PR resolves issue https://jira.ez.no/browse/EZP-23059

This implements semantic configuration configuration for RichText embeds and template tags.
Small changes are made to default embed and template tags configuration in order to make it more suitable for semantic configuration. Also default templates for embeds are removed as they were not really needed.

Previously field type configuration was handled by Content parser. This addition made tree building there quite big, so in order to make it more maintainable field type configuration parsing is moved to dedicated parsers, for the moment XmlText and RichText. They require `NodeBuilder` at the same position and also must not repeat same definitions. For that purpose `AbstractFieldTypeParser` is added, used to recognize field type parser and provide it with NodeBuilder at correct position.

Additionally this adds test fixtures for RichText custom XSL stylesheets.

Testing: unit tests + manual tests.
Yes, it refers to using "multi-level" keys below, like `fieldtypes.ezrichtext.output_custom_xsl`.