Add simple benchmark & a test framework (#2022)

See #2019, #2020 and #2021 for failed attempts at using a benchmark framework. So, for now I'll just go with timing the results manually. 

For trying this out:
- Backup your current account first, maybe there are some bugs in switching accounts.
- You can run benchmarks on either an emulated device or a real device. For better benchmark results, you should run the benchmark on a real device and make sure that the core is compiled in release mode.
- Disable animations on your device, otherwise the test may fail. (Developer options -> Window animation scale, Transition animation scale & Animatior duration scale -> set all three of them to 0x)
- In Android Studio: File -> Sync project with gradle files
- In Android Studio: Run -> Edit configurations -> `+` -> Android Instrumented test -> Either select a specific class or select "All in Module" -> OK -> Select your configuration in the toolbar -> Click on the green "run" button in the toolbar to run the tests

When the benchmark is done, you will get a result like `MEASURED RESULTS (Benchmark) - Going thorough all 10 chats: 11635,11207,11363,11352,11279,11183,11137,11145,11032,11057`, Paste `11635,11207,11363,11352,11279,11183,11137,11145,11032,11057` into a cell in a LibreOffice spreadsheet, do `Data -> Text to columns`, choose `,` as a separator, hit `OK`, and create a diagram.

gradle.properties

@@ -1,2 +1,2 @@
 android.enableJetifier=true
-android.useAndroidX=true
+android.useAndroidX=true