Fix AudioStreamPlayer icons, improve audio resource picker styling

[ckaiser]

Fixed AudioStreamPlayer/2D/3D icons not having their colors replaced by the icon loader, (same issue as in #91821, I searched in the files and this seems to be the last files with this issue, could be worth checking this in-code or pre-commit?).

Fixed the EditorStreamResourcePicker styling in light mode being broken and made some tweaks to it:

• Added a little more padding to the icon so it's not so close to the edge when the focus ring is around it
• Removed the colored rect that it was drawing around the preview, it looks better without it IMO
• Fixed it using the default font color when drawing the label

Before	After

[ckaiser]

Rebasing after the icons ended up getting fixed by #92766, so that leaves the background and margins.

[akien-mga]

Thanks!