Update Eigen to commit:66e8f38891841bf88ee976a316c0c78a52f0cee5

CHANGELOG
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66e8f3889 - Add architecture definition files for Qualcomm Hexagon Vector Extension (HVX)
2af700aa4 - Fix nullptr dereference in SVD.
86a43d8c0 - Fix clang-tidy warning

PiperOrigin-RevId: 552894986
Change-Id: I59cc553b1d4cbf8362d9f82882ffd737b416f86d
7 files changed