Refactor Godot Android architecture

[m4gr3d]

This PR sets the building blocks for a clean-up and re-architecture for the Godot Android platform integration.

The current architecture ties the Godot.java entry point to an Android Fragment component.
This is an improvement over the previous architecture where it was tied to an Android Activity component as it enables us to composite UI rendered by Godot with UI rendered by other frameworks. However this also limits the use of Godot on Android to Fragment-based apps, limits control over Godot's lifecycle since it's coupled to the Fragment's lifecycle, and limits usage of Godot on Android to a single window (Godot 4 supports multiple windows).

This PR starts by decoupling the Godot.java entry point from the Android Fragment component. A GodotFragment component is introduced to replicate the previous tied-to-Fragment lifecycle behavior and enable continuity for apps (including our own Godot Android Editor) that relies on that capability.

The changes should be transparent to Godot Android apps and games generated from the Godot Editor, and as such it targets Godot 4.1, so we can validate the new architecture and address any issues.
The work will continue in Godot 4.2 where we'll leverage the new capabilities offered by the architecture to enable support for multiple windows on Android and accelerate startup times for Godot apps and games on Android by leveraging Android Services to preload and prewarm the Godot Engine.

[YuriSizov]

Thanks!