[JEWEL-993] Add MacOS Scrollbar Detection to Standalone

[DanielSouzaBertoldi]

Context

After #3372 was merged, we finally have access to JNA in the :int-ui-standalone module. This means we can safely fetch data directly from MacOS settings and use it in our components 🥳

This PR basically just changes ScrollbarStyle.Companion.macOsLight() and ScrollbarStyle.Companion.macOsDark() to fetch the user's current option from the new StandaloneScrollbarHelper class instead of hardcoding an option.

I also added a minor bonus: now you can change the configurations of all scrollbars in our Scrollbar showcase, changing from "manual" mode to "system", check the screenshots below!

Changes

• Now that both StandalonePlatformCursorController and StandaloneScrollbarHelper use JNA to fetch style information, I opted to just move all JNA code from :decorated-window over to :int-ui-standalone, since the code we had there was more robust and :decorated-window depends on :int-ui-standalone anyway.
• Added new methods to Jewel's Foundation class so that we can add observers via JNA.
• Updated Scrollbars showcase code to add an option for scrollbars to follow the behavior/visibility of the system.
• Added a new icon called "Terminal"

Screenshots

Before	After
Screen.Recording.2026-02-04.at.15.04.24.mov	Screen.Recording.2026-02-04.at.14.55.50.mov

Scrollbars Showcase

Standalone	Bridge
Screen.Recording.2026-02-04.at.14.59.09.mov	Screen.Recording.2026-02-04.at.15.01.01.mov

[DanielSouzaBertoldi]

All code here was taken directly from com.intellij.ui.mac.foundation.Foundation.java class and converted to Kotlin.

However, I did not import 100% of the code there

[DanielSouzaBertoldi]

Unfortunately, as is the case with ScrollbarHelper from bridge, we can't directly use the code in MacScrollBarUI since all its classes are internal.

This means this code is duplicated. We have the same lines over in bridge, but such is the case with our structure. The only difference is that bridge uses IJP's version of Foundation.

[DanielSouzaBertoldi]

We can't set the vertical arrangement to spacedBy(16.dp) in our parent Column because that screws up the animation:

Screen.Recording.2026-02-04.at.15.21.51.mov

See? it kinda jumps at the end. That's because the parent Column has to get rid of the space that was reserved for the settings row after it's done animating :(

[nebojsa-vuksic]

We are missing tests :)

[DanielSouzaBertoldi]

@nebojsa-vuksic just pushed the changes you asked + added tests. However, to avoid having to add the JNA dependency in the test module, I had to make a bunch of changes to the code which in turn made it a bit more complex:

1. Created an interface that MacUtils implements, so that we can create a fake impl and use it in tests.
2. With the use of callbacks, StandaloneScrollbarHelper doesnt inherits from JNA

Like, I think this is still pretty okay overall, but let me know if you disagree (in other words, if you think it's a bit overkill)

[DanielSouzaBertoldi]

To avoid making StandaloneScrollbarHelper inherit from JNA and subsequently forcing us to add the JNA dependency in our int-ui-standalone-tests module, I had to move references to JNA's Callback here.

With the use of callbacks, we can make StandaloneScrollbarHelper refresh its state with whatever the callback returns. BUT! We have to do this "hacky" thing to keep the reference from being purged by GC 😭

[DanielSouzaBertoldi]

Please feel free to suggest better names if you think of any! 🙏🏻