[FEA]: Update standalone header testing to use installed version of CCCL

[jrhemstad]

Is this a duplicate?

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Area

Infrastructure

Is your feature request related to a problem? Please describe.

As a user and maintainer of CCCL, I want to be sure that all public headers are usable in an installed version of CCCL.

Today, CCCL tests all public headers can be #include <header> into an empty TU and compiled successfully.

However, this testing is done in the context of the GitHub repo, not the installed versions of the headers. This can cause problems if our install rules are misconfigured and forget to install some of the headers.

Describe the solution you'd like

We should update the per-header include testing for Thrust/CUB/libcu++ to work off an installed version of CCCL.

Describe alternatives you've considered

No response

Additional context

No response