Consider making DebugImagesLoader public

[markushi]

Problem Statement

For uses cases where sentry-native is initialized manually, both scope sync and the debug images loader need to manually configured.

Whilst adding the Scope observer works just fine:

options.addScopeObserver(new NdkScopeObserver(options));

Setting our default DebugImagesLoader doesn't work, as the class is package private.

options.setDebugImagesLoader(new DebugImagesLoader(options, new NativeModuleListLoader()));

Solution Brainstorm

Either expose a way to use the NDK without auto-init, or open up the DebugImagesLoader for public.

[markushi]

Let's add a comment to the class description that this requires manually initializing the SDK.