Textfield doesn't get focus when the user clicks it directly on the placeholder text

[Rick-Kirkham]

In TextField.ts, the _addListeners() method needs to be changed to add the code below that is either bolder or between two pairs of asterisks depending on whether Markdown syntax is working on GitHub today). Without this, the text field doesn't get focus when the user clicks it directly on the placeholder text.

if (this._type.indexOf(TextFieldConsts.Type.Placeholder) >= 0) {
        this._textField.addEventListener("focus", (event: MouseEvent) => {
          this._textFieldLabel.style.display = "none";
        });
    **// Ensure that the text box gets focus when the placeholder text itself is clicked.
        this._textFieldLabel.addEventListener("click", (event: MouseEvent) => {
          this._textField.focus();
        });**
        this._textField.addEventListener("blur", (event: MouseEvent) => {
          // Show only if no value in the text field
          if (this._textField.value.length === 0) {
            this._textFieldLabel.style.display = "block";
          }
        });
      }

Sorry, I can't make pull request because when I try to fork this repo, I get an erroneous message saying that I've already forked it.