eigen: modernize

Signed-off-by: Jack Nagel <jacknagel@gmail.com>
eigen 3.2.3

Signed-off-by: Jack Nagel <jacknagel@gmail.com>
eigen: install FindEigen3.cmake

Fixes #35225.
Closes #35243.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>
eigen: update 3.2.3 bottle.
Merge remote-tracking branch 'upstream/master'