Summary:
Depends on D19182. Ref T11015. This changes `path` from `text255` to `longtext` because paths may be arbitrarily long.
It adds `pathDisplay` to prepare for display paths and storage paths having different values. For now, `pathDisplay` is copied from `path` and always has the same value.
Test Plan:
- Ran migration, checked database for sanity (all `pathDisplay` and `path` values identical).
- Added new paths, saw `pathDisplay` and `path` get the same values.
- Added an unreasonably enormous path with far more than 255 characters.
Maniphest Tasks: T11015
Differential Revision: https://secure.phabricator.com/D19183
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