New Embed API

[amantoux]

Introduce a new API for embeds.

This change simplifies the configuration of SpanEmbeds & BlockEmbeds

Embeds must be registered in an EmbedRegistry that needs to be passed to the editor

[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 89.29%. Comparing base (61a029f) to head (dcfdec3).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #556      +/-   ##
==========================================
- Coverage   89.30%   89.29%   -0.02%     
==========================================
  Files          63       64       +1     
  Lines       10990    11039      +49     
==========================================
+ Hits         9815     9857      +42     
- Misses       1175     1182       +7     

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