ROU-12311: revert layer system regression with virtual select

[BenOsodrac]

This pull request addresses z-index layering issues for popups and overflow menus to ensure proper stacking behavior when popups are open. The main focus is on improving how popups and overflow menus interact visually, especially when multiple UI layers are present.

Layering and z-index adjustments:

• Changed the value of the --osui-popup-layer CSS variable from var(--layer-global-instant-interaction) to var(--layer-global-off-canvas) in _root.scss, aligning popups with other off-canvas elements for consistent stacking.
• Added a new CSS rule in _overflowmenu.scss that increases the z-index of .osui-overflow-menu__balloon.osui-balloon--is-open when a popup is open on the same screen, using the :has(.show-as-popup) selector to apply the layer exception.

Checklist

• tested locally
• documented the code
• clean all warnings and errors of eslint
• requires changes in OutSystems (if so, provide a module with changes)
• requires new sample page in OutSystems (if so, provide a module with changes)

[cssecautomation]

✅ Snyk checks have passed. No issues have been found so far.

Status	Scanner	Critical	High	Medium	Low	Total (0)
✅	Open Source Security	0	0	0	0	0 issues
✅	Licenses	0	0	0	0	0 issues
✅	Code Security	0	0	0	0	0 issues

💻 Catch issues earlier using the plugins for VS Code, JetBrains IDEs, Visual Studio, and Eclipse.

[cssecautomation]

✅ Snyk checks have passed. No issues have been found so far.

Status	Scanner	Critical	High	Medium	Low	Total (0)
✅	Licenses	0	0	0	0	0 issues
✅	Code Security	0	0	0	0	0 issues
✅	Open Source Security	0	0	0	0	0 issues

💻 Catch issues earlier using the plugins for VS Code, JetBrains IDEs, Visual Studio, and Eclipse.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud