Fix Android rendering, loading issues (#1090)

* Disable SLUG text band acceleration

* Load Android optional APIs dynamically

* Fixed the android-only Gauss-pane vertical flip by correcting render-target Y sampling in:

  - widgets/src/window.rs:110
  - widgets/src/gauss_view.rs:151

  Root cause: Gauss captures the scene into render-target textures, then samples them back
  into the UI. Those render-target textures need a Y flip when displayed, matching the
  existing Image widget behavior.