Multiselect overlay bug - baseZIndex property is unused

[rinukkusu]

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Current behavior
It's basically the same Bug as Dropdown overlay bug - baseZIndex property is unused in PrimeNG 12.2.0, but for the MultiSelect component.

When you're in a modal/dialog that's above zIndex 1000, then the Multiselect overlay opens below the dialog, no matter what you set for the baseZIndex property, since, looking at the actual source code, it's not being used. (https://github.com/primefaces/primeng/blob/master/src/app/components/multiselect/multiselect.ts#L684)

Expected behavior
The Multiselect component honors the baseZIndex setting and therefore renders above modals/dialogs with higher zIndex values.

Minimal reproduction of the problem with instructions
Have a modal with zIndex 2000 for instance and add a Multiselect with a baseZindex value that would render it above zIndex 2000.

What is the motivation / use case for changing the behavior?
The multiselect is unusable for containers with a high z-index since the overlay is hidden behind the container.

Please tell us about your environment:

• Angular version: 13.1.0

• PrimeNG version: 13.1.1

• Browser: all

• Language: all

• Node (for AoT issues): node --version = 16.13.1

[rinukkusu]

@cetincakiroglu duplicate PR, already open PR here: #11192