Improve Run-time File Saving and Loading demo (#1196)

- Add runtime MP3 and WAV loading with example files.
- Add runtime FBX loading (but no example files, due to known issues with
  the current FBX runtime loading implementation).
- Use supersampling for the 3D preview to further improve quality.
- Shorten file path to example glTF scene.
- Mention audio duration in the UI when loading an audio file.

loading/runtime_save_load/README.md

@@ -17,7 +17,8 @@ Can be loaded and saved at run-time:
 Can be loaded at run-time:
 
 - Images (TGA, BMP, SVG[^2])
-- Audio (Ogg Vorbis)
+- 3D scenes (FBX[^3])
+- Audio (Ogg Vorbis, MP3, WAV)
 - Fonts (TTF, OTF, WOFF, WOFF2, PFB, PFM, BMFont)
 
 [^1]: Manipulating custom binary formats is possible using the FileAccess and
@@ -27,6 +28,9 @@ PackedByteArray classes, but this is not shown in this demo.
 with `.svg` extension using the FileAccess class, but this is not shown in
 this demo.
 
+[^3]: There are known issues with runtime FBX loading, as mentioned in issue
+[#96043](https://github.com/godotengine/godot/issues/96043).
+
 See the [Saving and Loading (Serialization)](/loading/serialization/) demo for
 an example of saving/loading game progress.
 
@@ -42,7 +46,7 @@ Check out this demo on the asset library: https://godotengine.org/asset-library/
 
 ## Licenses
 
-- Files in `examples/3d_scenes/plastic_monobloc_chair_01_1k/` are copyright
+- Files in `examples/3d_scenes/gltf/` are copyright
   [Poly Haven](https://polyhaven.com/a/plastic_monobloc_chair_01)
   and are licensed under [CC0 1.0 Universal](https://creativecommons.org/publicdomain/zero/1.0/).
 - Files in `examples/audio/` are copyright [Red Eclipse](https://redeclipse.net)