* fix(recovery): snapshot a document only once it has unsaved edits
Opening a document lays it out, which bumps the scene version, so crash
recovery wrote a full .fig snapshot of every document opened from a file
without a writable source, edited or not. For the 401 MiB file from #924
that copied the whole archive a few seconds after opening and killed the
tab. Recovery now asks the document's change tracking, which ignores
layout, whether anything is unsaved.
* fix(recovery): store snapshots as Blobs so large documents fit
Chromium refuses a single IndexedDB value over 127 MiB, so a snapshot of
any larger document failed and recovery fell back to memory for the
rest of the session, holding another copy of the document. A Blob is
kept as a file at any size: a 421 MB snapshot now writes in IndexedDB.
Writes also no longer copy the archive first, and snapshots stored as
byte arrays by earlier versions still read back.
* test(recovery): drop the scene version from the large-buffer snapshot
6e68366bc6