Dropdown and MultiSelect converts filter value to lowercase

[donriver]

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https://www.primefaces.org/primeng/#/dropdown

Current behavior

Currently, all entered text in filter for drop down is converted to Lower Case.

Dropdown.prototype.onFilter = function (event) {
var inputValue = event.target.value.toLowerCase();
if (inputValue && inputValue.length) {
this.filterValue = inputValue;
this.activateFilter();
}
else {
this.filterValue = null;
this.optionsToDisplay = this.options;
}
this.optionsChanged = true;
};

Expected behavior
Leave text as it is.

Minimal reproduction of the problem with instructions

1. open showcase and select dropdown page (https://www.primefaces.org/primeng/#/dropdown)
2. go to "Content with Filters" case
3. open and type "B" in the filter

What is the motivation / use case for changing the behavior?
The customers want to see the entered text without any changes.

Please tell us about your environment:
Windows 10, VS Code

• Angular version: 5.X
  Angular 6.1.4

• PrimeNG version: 5.X
  PrimeNG 6.1.2
  Ultima themes engine 5.2.0

• 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 ]
  All browsers where this could be reproduced - not browser specific