Enable clippy::unnecessary_unwrap (#8756)

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

Release Notes:

- N/A

tooling/xtask/src/main.rs

@@ -112,7 +112,6 @@ fn run_clippy(args: ClippyArgs) -> Result<()> {
         "clippy::suspicious_to_owned",
         "clippy::type_complexity",
         "clippy::unnecessary_to_owned",
-        "clippy::unnecessary_unwrap",
         "clippy::useless_conversion",
         "clippy::useless_format",
         "clippy::vec_init_then_push",