Entity renderers should be given more data on render

[thibaudcolas]

Follow-up to #87. At the moment, entity components are only given a small amount of data about an entity for rendering:

draftjs_exporter/draftjs_exporter/entity_state.py

Lines 48 to 58 in 764d377

	props = entity_details['data'].copy()
	props['entity'] = {
	'type': entity_details['type'],
	}
	nodes = DOM.create_element()
	for n in self.element_stack:
	DOM.append_child(nodes, n)
	elt = DOM.create_element(opts.element, props, nodes)

There are a few more problems here:

• The shape of the props is different than how this is stored in the Draft.js entityMap.
• The entity data is given as the top-level props, which makes it impossible to add extra props without risking overwriting the entity data (say if the entity has a field called type that does something different from the entity type).

We should refactor this to something like:

props = {}
props['entity'] = entity_details
props['entity']['key'] = key
props['block'] = block
props['blocks'] = blocks
# (Potentially the `entity_range` as well?)

This way, it's easy to add arbitrary props without risking overwrites. The components get full access to the entity data, mutability, type, and key. And to the current block and blocks list, like styles, decorators, blocks.

Compared to the changes introduced in #90, this would be a breaking change, so should be considered carefully. Users of the exporter will have to rewrite their renderers slightly to use the new props shape.

[thibaudcolas]

If anyone is interested in contributing to this, I would welcome a pull request to implement this in a backwards-compatible way (the change just doesn’t feel worth breaking changes on its own).

We could use the following structure:

 props = entity_details['data'].copy() 
 props['entity'] = { 
     'type': entity_details['type'], 
+     'key': key, 
+     'entity': entity_details, 
+     'block': block, 
 } 

Then when we want to make this nicer / more future-proof as a breaking change, we can simply set props to equal that dict.