Rename the get_*() functions used as features in map_dep()

[damianooldoni]

As shown in #171, six get_*() functions are possible "values" of feature argument in map_dep(), while five other get_* functions are not. This is far from ideal. We would expect the same behavior for all get_* functions.

Proposal of @peterdesmet which I agree with: rename the get_*() functions used as feature values in map_dep() to summarize_*():

summarize_n_species
summarize_n_obs
summarize_n_individuals
summarize_rai
summarize_effort

Deprecation of the correspondent get_* functions is still possible of course.

To be discussed with @jimcasaer tomorrow

[damianooldoni]

This issue has been indirectly tackled during the camtraptor July 2023 coding sprint. See all new issues made by @peterdesmet starting with "Rename" or "Combine".