[Embeddables Rebuild] Delete Legacy Embeddable Framework

[ThomThomson]

Problem

blocked on #180059

Once all usages of the legacy Embeddable framework are converted to the new framework, including Dashboard, we will need to remove the legacy embeddable framework entirely, including all examples and unit tests.

Note: This must not include the serverside embeddable migrations, as these might still be needed when upgrading a cluster from a version before the clientside migrations were introduced (~8.13).

Tasks

• Remove embeddable.registerEmbeddableFactory, preventing legacy embeddable registration - small
• Update dashboard "Add from library" to remove usage of legacy embeddables - small
• Update dashboard "Add panel" to remove usage of legacy embeddables - small
• Update Canvas "Add from library" to remove usage of legacy embeddables - small
• Update Canvas "Add panel" to remove usage of legacy embeddables - small
• Remove usage of getEmbeddableFactory in DashboardContainer.addNewPanel - small
• Remove usage of getEmbeddableFactory in DashboardRenderer - small
• Remove usage of getEmbeddableFactory in migrateDashboardInput - medium. Question: how will migrations be run for legacy panels replaced by new react embeddable panels?
• Remove legacy embeddable registry and getter methods - small
• Refactor DashboardContainer so that it no longer implements Container interface - [Embeddables Rebuild] Migrate Dashboard embeddable to plain javascript object #197281
• Remove Container interface - small
• Remove Embeddable interface and all associated types like EmbeddableInput and EmbeddableOutput - large since there may be unexpected usages of these classes throughout Kibana.