Enable clippy::vec_init_then_push (#8771)

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

Release Notes:

- N/A

tooling/xtask/src/main.rs

@@ -108,7 +108,6 @@ fn run_clippy(args: ClippyArgs) -> Result<()> {
         "clippy::suspicious_to_owned",
         "clippy::type_complexity",
         "clippy::unnecessary_to_owned",
-        "clippy::vec_init_then_push",
     ];
 
     // When fixing violations automatically for a single package we don't care