transform locked file links in offline exports
transform locked file links in offline exports

If a file is locked and is linked to by some content, also transform
those links so offline content can handle it appropriately.

refs OFFW-153

test plan:
* see g/106416

Change-Id: Ia68a17f8179bcc6c5f1ad58b9a45f4fb8c3fade0
Reviewed-on: https://gerrit.instructure.com/106431
Tested-by: Jenkins
Reviewed-by: Mysti Sadler <431d062aff1e8f25416b3a7b732fe6effdb03f9a@instructure.com>
QA-Review: Nathan Rogowski <2e8aa918660411855c6d44d5bb2da677aa033255@instructure.com>
Product-Review: Jon Willesen <0321efbc0acf6204eb6035acb1d418838b450d08@instructure.com>

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