[NUI] Support markup anchor to TextLabel, TextField, TextEditor (#2813)

[NUI] Support markup anchor to TextLabel, TextField, TextEditor (#2813)

* [NUI] Support markup anchor to TextLabel, TextField, TextEditor

User can set href on anchors using the anchor tag <a> in markup.
and also can register AnchorClicked callback in Text components.
the AnchorClicked signal is emitted when the anchor is clicked.

example:
label.Text = "<a href='https://www.tizen.org'>Tizen</a>";
label.EnableMarkup = true;
label.AnchorClicked += (sender, e) =>
{
  Tizen.Log.Info("NUI", e.Href + "\n");
};

Signed-off-by: Bowon Ryu <bowon.ryu@samsung.com>
[NUI] Remove unnecessary codes.

Signed-off-by: Bowon Ryu <bowon.ryu@samsung.com>
* [NUI] Change the name of signal to AnchorClicked.

To prevent confusion with TouchSignal(),
the name of signal was changed to AnchorClicked.

Signed-off-by: Bowon Ryu <bowon.ryu@samsung.com>