Accessibility: p-dropdown does not contain children with role=option

[paraskt]

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Current behavior
p-dropdown must contain children with role=option. As per following certain ARIA roles must contain particular children.
https://dequeuniversity.com/rules/axe/2.6/aria-required-children

Expected behavior
p-dropdown must contain children with role option. This will cause screen readers to not know about how many elements are there in the dropdown/listbox
For each role, WAI-ARIA explicitly defines which child and parent roles are allowable and/or required. ARIA roles missing required child roles will not be able to perform the accessibility functions intended by the developer.

Minimal reproduction of the problem with instructions

What is the motivation / use case for changing the behavior?
For each role, WAI-ARIA explicitly defines which child and parent roles are allowable and/or required. ARIA roles missing required child roles will not be able to perform the accessibility functions intended by the developer.

Please tell us about your environment:

• Angular version: 5.X
  5.1.3

• PrimeNG version: 5.X
  5.2.5

• Browser: [all | Chrome XX | Firefox XX | IE XX | Safari XX | Mobile Chrome XX | Android X.X Web Browser | iOS XX Safari | iOS XX UIWebView | iOS XX WKWebView ]
  Chrome, edge

• Language: [all | TypeScript X.X | ES6/7 | ES5]

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