This is a helper to allow srvyr's syntactic style. In particular, it tells
functions inside of a summarize call what survey to use (for the current
cur_svy() or the complete survey for
In general, users will not have to worry about getting (or setting) the current
context's survey, unless they are trying to extend srvyr.
vignette("extending-srvyr") for more details.
is deprecated, but returns the same value as
cur_svy() cur_svy_full() current_svy()
a tbl_svy (or error if called with no survey context)