Switch the theme for GodotPanelApp to match the one used by GodotApp

[m4gr3d]

GodotPanelApp is only included in the manifest from a Godot editor build, so we can assume that when it's enabled, GodotApp and its theme resources will always be available.

[m4gr3d]

@dsnopek This also addresses a build issue that occurs when using the vendors plugin library in an Android project that doesn't have a dependency on the splashscreen library.

[dsnopek]

Seems fine!

This also addresses a build issue that occurs when using the vendors plugin library in an Android project that doesn't have a dependency on the splashscreen library.

Don't we require the splashscreen library? I'm not sure I understand how a Godot Android app wouldn't depend on it

That said, having less stuff is good :-)

[m4gr3d]

Don't we require the splashscreen library? I'm not sure I understand how a Godot Android app wouldn't depend on it

The splashscreen library is added as an implementation dependency for the plugin, so it's included automatically both at compile-time and runtime.

What's not included however are the splashscreen library resources that define the postSplashScreenTheme theme attribute. So when another project with a dependency to the vendor plugin library tries to compile without a dependency to the splashscreen library, the missing theme attribute definition causes a build error.