nrow_subset_linter() should be pipeline-aware

[MichaelChirico]

x |>
  subset(conds) |>
  nrow()

And, assuming #2313,

x |>
  filter(conds) |>
  nrow()

[MichaelChirico]

Copying over test cases:

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