Failure to compile with --cfg tokio_unstable and the process and rt features enabled

[Noah-Kennedy]

If using the unstable features with only the process and rt features enabled, tokio will fail to compile:

noah@resf-attack-drone ‹ master ●●● › : ~/CLionProjects/smoke
[0] % cargo check
    Checking tokio v1.18.2
error[E0432]: unresolved import `crate::runtime::IoDriverMetrics`
  --> /home/noah/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.18.2/src/io/driver/metrics.rs:20:24
   |
20 |         pub(crate) use crate::runtime::IoDriverMetrics;
   |                        ^^^^^^^^^^^^^^^^---------------
   |                        |               |
   |                        |               help: a similar name exists in the module: `WorkerMetrics`
   |                        no `IoDriverMetrics` in `runtime`

error[E0282]: type annotations needed
   --> /home/noah/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.18.2/src/io/driver/mod.rs:303:18
    |
303 |             self.inner().map(|inner| f(&inner.metrics))
    |                  ^^^^^ cannot infer type
    |
    = note: type must be known at this point

error[E0599]: no method named `inner` found for reference `&io::driver::Handle` in the current scope
   --> /home/noah/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.18.2/src/io/driver/mod.rs:303:18
    |
303 |             self.inner().map(|inner| f(&inner.metrics))
    |                  ^^^^^-- help: remove the arguments
    |                  |
    |                  field, not a method

Some errors have detailed explanations: E0282, E0432, E0599.
For more information about an error, try `rustc --explain E0282`.
error: could not compile `tokio` due to 3 previous errors

I ran a bisect and found it was introduced here:

769fb1547fc50406fc2adb23cdf17a1aaf5744ac is the first bad commit
commit 769fb1547fc50406fc2adb23cdf17a1aaf5744ac
Author: Lucio Franco <[email protected]>
Date:   Thu Feb 24 13:39:37 2022 -0500

    tokio: Add initial io driver metrics (#4507)

 .gitignore                           |  2 +
 tests-integration/Cargo.toml         |  2 +-
 tokio/src/io/driver/metrics.rs       | 22 +++++++++
 tokio/src/io/driver/mod.rs           | 38 +++++++++++++++-
 tokio/src/lib.rs                     |  2 +-
 tokio/src/macros/cfg.rs              |  6 +++
 tokio/src/runtime/metrics/io.rs      | 30 +++++++++++++
 tokio/src/runtime/metrics/mod.rs     |  5 +++
 tokio/src/runtime/metrics/runtime.rs | 87 ++++++++++++++++++++++++++++++++++++
 tokio/src/runtime/mod.rs             |  4 ++
 tokio/tests/rt_metrics.rs            | 34 ++++++++++++++
 11 files changed, 229 insertions(+), 3 deletions(-)
 create mode 100644 tokio/src/io/driver/metrics.rs
 create mode 100644 tokio/src/runtime/metrics/io.rs

Compilation is only successful with the net feature.