resetFilter function for Dropdown

[nsksaisaravana]

[ ] bug report
[* ] feature request
[ ] support request => Please do not submit support request here, instead see https://forum.primefaces.org/viewforum.php?f=57

**Codesandbox Case (Bug Reports)**
Please fork the codesandbox below and create a case demonstrating your bug report. Issues without a codesandbox have much less possibility to be reviewed.

https://codesandbox.io/s/qjx332qq4

**Current behavior**
No function to clear the dropdown filter text box

**Expected behavior**
Nee a function to clear the dropdown filter text box

**Minimal reproduction of the problem with instructions**
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**Please tell us about your environment:**
<!-- Operating system, IDE, package manager, HTTP server, ... -->

* **React version:**
React versoin : 16.8.5

* **PrimeReact version:**
PrimeReact 3.4.0

* **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 ]
Browser Chrome 56
 
* **Language:** [all | TypeScript X.X | ES6/7 | ES5]
Typescript : 3.3