Enable clippy::filter_map_identity (#8741)

This PR enables the
[`clippy::filter_map_identity`](https://rust-lang.github.io/rust-clippy/master/index.html#/filter_map_identity)
rule and fixes the outstanding violations.

Release Notes:

- N/A

tooling/xtask/src/main.rs

@@ -95,7 +95,6 @@ fn run_clippy(args: ClippyArgs) -> Result<()> {
         "clippy::explicit_auto_deref",
         "clippy::explicit_counter_loop",
         "clippy::extra_unused_lifetimes",
-        "clippy::filter_map_identity",
         "clippy::identity_op",
         "clippy::implied_bounds_in_impls",
         "clippy::iter_kv_map",