Also update the gitignore to ignore the '.cxx' directory AGP 3.5.0
uses for native build artifacts.

Signed-off-by: Harsh Shandilya <me@msfjarvis.dev>

Signed-off-by: Eric Kuck <eric@bluelinelabs.com>

This change avoids all need for changing any file under
VCS to insert signing keys and configs for release builds.

Example contents of keystore.properties

```
// Location of keystore, relative to module build.gradle,
// in this case, of the app module
storeFile=../wireguard.jks
storePassword=b3ty0uc4nth4xxth1s
keyAlias=wireguard
keyPassword=4ndr01dsux
```

Signed-off-by: Harsh Shandilya <me@msfjarvis.dev>

Having a consistent set of code style and inspection rules makes it
easier for contributors to match the existing code.

Signed-off-by: Samuel Holland <samuel@sholland.org>

Signed-off-by: Samuel Holland <samuel@sholland.org>

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>