Migrate canvas plugin system to New Platform

[stacey-gammon]

Canvas introduced a new mechanism for users to write plugins (something like dropping function definitions in a folder, I think). This is different than the current way we expect users to write plugins.

We should:

• Figure out if Canvas can use the current system rather than introduce a new one
• If there is a legitimate reason for Canvas to use a new system, can it be integrated into the current system, possibly only in New Platform, so it's an officially supported plugin mechanism in core?

We should do this before we GA. Once users start writing plugins using this new method, it will be harder to consolidate the approaches, if we want to continue supporting the plugins that were written in the interim.

cc @epixa @elastic/kibana-canvas

[stacey-gammon]

We decided to move forward with a new platform migration, however, it looks like there are some dependencies blocking this effort, and it will likely be a lot of work, so removing the 7.0 and blocker labels, though this will be a blocker for Canvas GA.

[stacey-gammon]

related:

• Meta issue for visualizations using the expression language: Use the Canvas rendering pipeline/expressions for all visualizations #19813
• Blocker issue with the current setup, in that will import disabled plugins functions: Interpreter plugin imports from other plugins #29324
• Blocker issue with visualizations not being available outside default space: User cannot create or view visualizations outside of default space #27257

[elasticmachine]

Pinging @elastic/kibana-app

[cqliu1]

Closing this issue since Canvas doesn't use a separate plugin system anymore.