Change the return type of AccessValues::size() to be view-like

[aprokop]

This also fixes a recently introduced warning (#1180).

[dalg24]

Views use size_t regardless of the backend.
(Just picking on the PR title)

[dalg24]

This also fixes a recently introduced warning.

Please paste the warning you are referring to.
It's unclear that the changes proposed are the right thing to do with the information provided so far.

[aprokop]

Please paste the warning you are referring to.

In ArborX_SpaceFillingCurves.hpp:75:

comparison of integers of different signs:
'size_t' (aka 'unsigned long') and 'typename View *, Device>::size_type' (aka 'int')
[-Wsign-compare]
ARBORX_ASSERT(linear_ordering_indices.size() == values.size()); ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~