Support Android Direct Boot

### Problem Statement

Reference: https://developer.android.com/training/articles/direct-boot

In Direct Boot mode, the Sentry cache path needs to be set to Device Encrypted (DE) storage (see #2052).

```csharp
.UseSentry(options =>
{
#if ANDROID
var deviceContext = Platform.AppContext.CreateDeviceProtectedStorageContext();
options.CacheDirectoryPath = deviceContext?.CacheDir?.AbsolutePath;
#endif
})
```

Direct Boot is an Android 7+ feature (API 24, "N"), so it also requires the app to either set:

```xml
24.0
```

... or check at runtime, such as with:

```csharp
#if ANDROID
#pragma warning disable CA1416
if (global::Android.OS.Build.VERSION.SdkInt >= global::Android.OS.BuildVersionCodes.N)
{
var deviceContext = Platform.AppContext.CreateDeviceProtectedStorageContext();
options.CacheDirectoryPath = deviceContext?.CacheDir?.AbsolutePath;
}
#pragma warning restore CA1416
#endif
```

### Solution Brainstorm

Since Direct Boot is only allowed when `android:directBootAware` is in the app manifest, it should be possible to detect it and automatically set the correct cache path as the default.

Stretch goal: It appears there's a way to detect [when the user unlocks the device](https://developer.android.com/training/articles/direct-boot#notification), at which time it would be possible to move the cache back to its regular location in CE storage. That would require a bit of coordination though, as we currently don't have a mechanism to change cache paths once the SDK is initialized. It would have to start writing to the new cache but continue to read from the old until drained.