update bugsnag-android dep to v6.8.0

[richardelms]

Goal

Update the bugsnag-android dependency to v6.8.0

Changeset

• Update gradle build references to bugsnag-android to v6.8.0.
• Convert discardClasses and redactedKeys to Regex patterns when sending to the android layer.
• Remove references to ThreadType, replace required ones with refs to ErrorType.
• Convert the getThreadId and setThreadId JNI refs to the new string signatures.
• The Unreal layer no longer handles auto session tracking due to improvements in the android notifier.

Testing

• Updated existing tests to match the changed data types.
• Updated the fixture to clear the new bugsnag cache location

[twometresteve]

Looks fine from my perspective.

[lemnik]

LGTM