Fix ColorPicker margin theme property

[KoBeWi]

Fixes #62937
Supersedes #76567

Changing the base type would break compatibility, so instead I just added another VBoxContainer inside MarginContainer inside ColorPicker. This is the rare occurrence where node's internal structure changes.

[TheSecondReal0]

Tested and seems to work, what is the margin theme override supposed to do after this PR?
Also thanks for opening an improved version of my PR, really appreciate it and would love for this bug to get fixed!

[KoBeWi]

margin adds a margin (padding?) around the ColorPicker. The previous implementation was supposed to do the same, but it wasn't implemented correctly.

[TheSecondReal0]

Not sure how you tested or if it's meant to work this way but I just tried putting multiple colorpickers into an HBoxContainer and changing the margin override did nothing. Without this PR it moves the colorpicker down and to right without claiming more space which is also incorrect.

[KoBeWi]

Works correctly for me

godot.windows.editor.dev.x86_64_1Knf3ENqMj.mp4

[TheSecondReal0]

Huh, I'll recompile and retest soon. If I get different results again I'll post a scene/project file, could you post yours?

[KoBeWi]

Pretty sure it works in a fresh project.

[YuriSizov]

Seems pretty straightforward. The original implementation looks super weird.

[akien-mga]

Thanks!