[SuperEditor] - Let users anchor popovers near text tokens

[matthew-carroll]

Users should be able to display arbitrary popovers near a text token, e.g., "@someuser", "#someHashTag".

This ticket depends on a couple others:

• Tokenization reactions: [SuperEditor] - Hashtags and @-mentions #1077
• Generic anchor system: Add an anchor system to SuperEditor widget #424

[matthew-carroll]

CC @miguelcmedeiros @jmatth

[matthew-carroll]

CC @Jethro87