GD-254: Fix inspector icon scaling

[MikeSchulze]

Orignal PR created by bitbrain

Why

On 4K monitors especially, the icons are too small and do not scale properly with the Godot editor.

What

• Updated the inspector image import settings to ensure icons now are displayed correctly by set editor/scale_with_editor_scale=true
• Fix tree item icons by replace the manual scaling by setting scaling property theme_override_constants/icon_max_width=16x<scale_factor>

before

after

[MikeSchulze]

@bitbrain can you verify if this fix working on your 4k monitor?

[bitbrain]

beautiful, works like a charm!