cmake: use find_package(OpenEXR) to support OpenEXR 3+

[alalek]

Validation:

• Fedora 35 with openexr-devel package (3.1.3-1)
• Fedora 35 with openexr2-devel package (2.5.5-4) - legacy way without find_package() adding version in find_package(OpenEXR 3) breaks detection script again (won't fix for now).

TODO:

• Mac builder: BUILD_OPENEXR = was ON, now OFF, so auto-detection script is launched. Added HAVE_CXX11 check

force_builders=Custom,Custom Win,Custom Mac

build_image:Custom=ubuntu-openvino-2021.4.0:20.04
Xbuild_image:Custom=ubuntu-openvino-2021.3.0:20.04
Xbuild_image:Custom=ubuntu-openvino-2021.2.0:20.04
Xbuild_image:Custom=ubuntu-openvino-2020.3.0:16.04
build_image:Custom Win=openvino-2021.4.2
Xbuild_image:Custom Win=openvino-2021.3.0-vc16
build_image:Custom Mac=openvino-2021.4.0

test_modules:Custom=dnn,python2,python3,java
test_modules:Custom Win=dnn,python2,python3,java
test_modules:Custom Mac=dnn,python2,python3,java

buildworker:Custom=linux-1
test_opencl:Custom=ON
test_bigdata:Custom=1
test_filter:Custom=*

buildworker:Custom Win=windows-3
test_opencl:Custom Win=ON
test_bigdata:Custom Win=1
test_filter:Custom Win=*

[alalek]

👍