nrow_subset_linter() should recognize filter() usage as well

[MichaelChirico]

nrow(filter(x, conds))

This is basically the same as nrow(subset(x, conds)).

[MichaelChirico]

Copying over test cases:

lintr::expect_lint(
  "nrow(dplyr::filter(x, y == z))",
  "Use arithmetic to count the number of rows satisfying a condition",
  nrow_subset_linter
)