Implement dynamic scaling of the LineEdit right icon based on control size and scale factor

[nongvantinh]

Close: https://github.com/godotengine/godot-proposals/issues/10493

The implementation allows the LineEdit node to scale the right icon to match the font size first. Then, when the expand_icon option is enabled, the icon will expand to the full height of the node. The scale of the icon can then be controlled using the scale factor.

https://github.com/user-attachments/assets/bed11cde-9424-4f0f-9d6a-d7145eb40dda

[KoBeWi]

Right Icon Scale has no effect when Expand Icon is off. It should be disabled in that case.

[KoBeWi]

This changes the default behavior of the right icon. It will scale to text, while previously it would use original size. I think the behavior should be preserved. You can change expand_icon to expand_mode enum and allow all 3 behaviors (original size, fit to text and fit to LineEdit).

[Repiteo]

Needs rebase

[nongvantinh]

This PR is older than my entire volatile memory.

[Repiteo]

Thanks!