Upgrade to a-c 27 and use glean plugin

[psymoon]

Vision statement / What / Requirements

Spawned from #2992 (comment), the way that we import glean plugin is deprecated. We should address this shortly after the 4.7 release to mitigate the problem of generating the wrong glean dependency code re-occuring in the future.

Impact

FFTV + Glean may not work as intended unexpectedly in the future (because sdk_generator.gradle script has no way to ensure that it's running the correct version of the Glean generator).

Acceptance criteria

a-c dependency is updated to 27 and we use `apply plugin: "org.mozilla.telemetry.glean-gradle-plugin".