cmake: Export namespaced library targets

[ethanmusser]

Update CMake to export namespaced targets, conforming to the modern library standard practice. Behavior is preserved for consumers using the legacy, unnamespaced targets via new interface libraries generated in the package configuration files. Also update all in-library links to use the namespaced targets.

Now, users of LibMultiSense will consume it as follows.

find_package(MultiSense)
add_library(MyLib my_lib.cpp)
target_link_libraries(MyLib PRIVATE MultiSense::MultiSense)

Resolves #306.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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