Migrate Legacy Libraries Flow

[sdaitzman]

Tracker story for the migrate legacy libraries flow.

Figma link, and mockups included under sub-issues.

Spec

The user can select a set of legacy/v1 libraries, and is guided through the process of migrating those libraries to the new libraries experience.

1. Legacy v1 libraries become collections in v2 libraries when selected for migration.
2. The flow allows users to choose an arbitrary number of v1 libraries as migration source, and exactly one v2 library as migration destination.

[sdaitzman]

All search/sort/filters for legacy libraries listings are low-priority to implement except for unmigrated/migrated filter.