- This also fixes the HistoryStorageSuggestionProvider to dedupe
history suggestions based on the ID, picking the one with the
highest score.

- Should other providers still return suggestions with duplicate
IDs we now throw an exception containing the provider class name.
Co-authored-by: Grisha Kruglov <gkruglov@mozilla.com>

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prompts.

The Experiments library should update it's experiments list from Kinto automatically & async on initialization.

This requires some larger changes, specifically:
- Introduced `ExperimentsUpdater`, which intends to contain the experiments update logic & scheduling.
- It does not contain periodic updating of experiments yet (to reduce the scope here, i broke this out to [this bug](https://bugzilla.mozilla.org/show_bug.cgi?id=1541973)).
- Added Experiments integration & initialization to the Glean sample app. This allows us testing app integration.
- Require `Glean` to be initialized first, before Experiments.
- On library init (`Experiments.initialize()`)
- automatically load experiments from storage
- automatically start async updating of the experiments list from the server (from Kinto, triggered by `ExperimentsUpdater`)
- Restructure the testing/mocking approach & clean up `ExperimentsTest.kt` significantly.
- Most importantly, make `ExperimentsInternalAPI` testable through instances & don't use the `Experiments` singleton in tests.
- Set up standard mocks that reduce the setup code for most of the tests in `ExperimentsTest.kt`.
- Make `ExperimentsUpdater` waitable on it's async update task for tests.
- Cleanups:
- Delete the alternative `JobService`-based scheduler implementation.
- Flatten the `ExperimentSource` and `ExperimentStorage` hierarchies. They just have one implementation now and are not configurable from library users.
- Move the `evenDistribution()` test over to a more fitting test file.
- Do a first pass on `README.md`, mostly removing parts that don't apply anymore.

State: mozilla-l10n/android-l10n@932938a1cae1ba6f84f79723dd7980486fef223f

Issue #2487: update_geckoview.sh: Add support for updating all GeckoView channels (nightly, beta, release).