Use Upstream Eigen3Config.cmake

[sloretz]

The chocolatey package for Eigen currently ships a custom EigenConfig.cmake, but it only sets old-style CMake variables. The upstream EigenConfig.cmake sets CMake targets. I think the upstream one should be used here.

This repo's

choco-packages/package/eigen/share/cmake/Eigen3Config.cmake

Lines 1 to 6 in 45edd84

	get_filename_component (_PREFIX "${CMAKE_CURRENT_LIST_DIR}/../.." ABSOLUTE)
	set (Eigen3_INCLUDE_DIRS "${_PREFIX}/include")
	# Compatibility with nonstandard and legacy package variable expectations.
	set (Eigen3_INCLUDE_DIR "${Eigen3_INCLUDE_DIRS}")
	set (EIGEN3_INCLUDE_DIRS "${Eigen3_INCLUDE_DIRS}")
	set (EIGEN3_INCLUDE_DIR "${Eigen3_INCLUDE_DIRS}")

Upstream's
https://gitlab.com/libeigen/eigen/-/blob/master/cmake/Eigen3Config.cmake.in#L7