[hooks] base64-encode extid before inserting it into moved_entities If we insert the wrong value we're never going to find these entities again... Closes #5741105.

Release notes
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.. toctree::
    :maxdepth: 1

    3.21
    3.20
    3.19
    3.18
    3.17
    3.16
    3.15
    3.14