work around erroneous "undefined in device code" error in basic_any

[ericniebler]

Description

this PR addresses an issue in `basic_any` that was causing nvcc to erroneously think that certain host-only entities were needed in device code, leading to an error.

the code was using the value of a host-only member function pointer in a host-only constexpr function. something about how this function was getting used in some code i was working on made nvcc think the member function was also needed on device. i have not been able to isolate the source of the problem, so i can't provide a test case for it, unfortunately.

this PR changes the constexpr function to a type computation, with the member function pointer as a NTTP. that seems to mollify nvcc.

[github-actions]

🟩 CI finished in 58m 18s: Pass: 100%/20 | Total: 1h 59m | Avg: 5m 59s | Max: 14m 56s | Hits: 297%/522

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👃 Inspect Changes

Modifications in project?

	Project
	CCCL Infrastructure
	libcu++
	CUB
	Thrust
+/-	CUDA Experimental
	python
	CCCL C Parallel Library
	Catch2Helper

Modifications in project or dependencies?

	Project
	CCCL Infrastructure
	libcu++
	CUB
	Thrust
+/-	CUDA Experimental
	python
	CCCL C Parallel Library
	Catch2Helper

🏃‍ Runner counts (total jobs: 20)

#	Runner
12	linux-amd64-cpu16
4	linux-arm64-cpu16
2	windows-amd64-cpu16
2	linux-amd64-gpu-rtx2080-latest-1