This also upgrades the vendored Glean version, which thanks to our
upstream work doesn't change anything else (except one small
Mozilla-developed dependency)
It's still feature-gated to nightly.
In C++ there's now a `MOZ_GLEAN` define.
For Rust it's behind the `glean` feature (enabled on nightly only).
The `fog` crate is empty, so no Glean is actually instantiated.
Differential Revision: https://phabricator.services.mozilla.com/D68539
--HG--
rename : third_party/rust/glean-preview/src/metrics/mod.rs => toolkit/components/glean/src/lib.rs
extra : moz-landing-system : lando
1a47da3ae3