Add except= parameter to `xml_find_function_calls()

[AshesITR]

          conjugate `function_names`, i.e. `function_names` sets which calls to _include_, this sets which calls to _exclude_. Then in this step we can do `$xml_find_function_calls(exclude = except)`, done.

We could also use it in return_linter():

lintr/R/return_linter.R

Line 94 in 0f0b17c

except <- union(special_funs, except)

Originally posted by @MichaelChirico in #2357 (comment)

[AshesITR]

Duplicate of #2429