Refactoring/dpctl tensor type dispatch namespace

[oleksandr-pavlyk]

This PR moves type dispatching types from dpctl::tensor::detail to dpctl::tensor::type_dispatch namespace.

Incidentally, it also removes static definition of function pointer arrays from include/kernels/boolean_indexing.hpp.
They are actually also defined source/boolean_indexing.cpp.

This change will likely require code changes in downstream projects using "dpctl4pybind11.hpp".

This PR is the foundation for the further work on unary functions and reductions, so I'd appreciate a prompt review.

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[coveralls]

Coverage: 83.263%. Remained the same when pulling 0ab2223 on refactoring/dpctl-tensor-type-dispatch-namespace into 4e41318 on master.

[github-actions]

View rendered docs @ https://intelpython.github.io/dpctl/pulls/1179/index.html

[github-actions]

Array API standard conformance tests for dpctl=0.14.3dev1=py310h76be34b_3 ran successfully.
Passed: 120
Failed: 887
Skipped: 109

[antonwolfy]

I've checked dpnp build with #1383 and no issue.

[github-actions]

Deleted rendered PR docs from intelpython.github.com/dpctl, latest should be updated shortly. 🤞

[github-actions]

Array API standard conformance tests for dpctl=0.14.3dev1=py310h76be34b_3 ran successfully.
Passed: 120
Failed: 887
Skipped: 109