Stretch mode and expand mode fixes

[Variable-ind]

(NOTE: i've moved the extra changes to separate prs, ythis pr now only contains stretch and expand fixes)

• Fixed expand mode of export preview.
• Changed occurrences of stretch_mode = 6 to stretch_mode = 5 (Reason: in Godot 3 the index for keep aspect centered was 6 but in Godot 4, it was moved to index 5)
  • Brush select buttons
  • Pattern select buttons
  • Tool brush preview button (BaseDraw and PaintSelect),
  • Bucket pattern button
  • ShowAnimate icon in ImageEffectParent.tscn at VBoxContainer/ShowAnimate
  • Start, Settings, OpenFolder icon at Recorder.tscn
• Fixed incorrect resizing of backgroung transparent checker of effects ImageEffectParent.tscn, ResizeCanvas.tscn ShaderEffect.tscn
  • TransparentChecker is now a direct child of AspectRatioContainer, and stretch_mode for Preview is set to 5

[OverloadedOrama]

Thanks!