Dropdown - Enable typing into field

As a user
I can type to filter items in a Dropdown
so I can find an item in a long list

---

*Dev notes*

No need to implement the searching algorithm.
Just enable typing into the input and add event listeners. Client will handle reducing the list.

Add the following props to Dropdown:
```
/**
* Enables user to focus and type into the dropdown text field
*/
hasTextEntry: PropTypes.bool,
/**
* Called when user puts focus on the dropdown text field
*/
onTextEntryFocus: PropTypes.func,
/**
* Called when user puts focus away from the dropdown text field
*/
onTextEntryBlur: PropTypes.func,
/**
* Called when user types into the dropdown text field
*/
onTextEntryChange: PropTypes.func,
```

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_Requested by Punit from Fusion Production_