SpriteFramesEditor: preserve source texture margins when creating frames from AtlasTexture

[kleonc]

When creating frame from AtlasTexture its margin was ignored which can result in incorrect rendering.

Tested with MRP from #42806.
Source AtlasTexture:

Created frames:

• 3.3.2-stable:
  

[sub_resource type="AtlasTexture" id=1]
flags = 4
atlas = ExtResource( 1 )
region = Rect2( 4, 132, 16, 16 )

[sub_resource type="AtlasTexture" id=2]
flags = 4
atlas = ExtResource( 1 )
region = Rect2( 20, 132, 16, 16 )

[sub_resource type="AtlasTexture" id=3]
flags = 4
atlas = ExtResource( 1 )
region = Rect2( 36, 132, 16, 16 )

[sub_resource type="AtlasTexture" id=4]
flags = 4
atlas = ExtResource( 1 )
region = Rect2( 52, 132, 16, 16 )

• This PR:
  

[sub_resource type="AtlasTexture" id=1]
atlas = ExtResource( 1 )
region = Rect2( 4, 132, 15, 16 )
margin = Rect2( 1, 0, 1, 0 )

[sub_resource type="AtlasTexture" id=2]
atlas = ExtResource( 1 )
region = Rect2( 19, 132, 16, 16 )

[sub_resource type="AtlasTexture" id=3]
atlas = ExtResource( 1 )
region = Rect2( 35, 132, 16, 16 )

[sub_resource type="AtlasTexture" id=4]
atlas = ExtResource( 1 )
region = Rect2( 51, 132, 14, 16 )
margin = Rect2( 0, 0, 2, 0 )

[akien-mga]

Thanks!

[akien-mga]

Does this fix #42806?

[kleonc]

Does this fix #42806?

No, this PR only fixes preserving margins when creating frames from an AtlasTexture. Issue in #42806 happens when you:

1. Create SpriteFrames with a source being a non-AtlasTexture texture. Frame regions won't have any margins because source texture has no margins.
2. Then change import settings of that source texture so it will be imported as an AtlasTexture (combining it with other textures into spritesheet). Resulting AtlasTexture the SpriteFrames is referencing can now have some margins added because of packing optimization (transparent borders aren't stored directly in the generated spritesheet) but the frame regions in SpriteFrames are still unchanged.