Update Eigen to commit:bb73be8a2e8da00c1cf5d26acb9fe47a87b8047f

CHANGELOG
=========
bb73be8a2 - make fixed-size objects trivially move assignable

PiperOrigin-RevId: 693468343
Change-Id: Ic28e61d86a09b47f93ebc1edb70b370ca21c3061
7 files changed