Fixed right text selection handle is not moved after left text selection handle is...

Fixed right text selection handle is not moved after left text selection handle is selected.

[Title] Fixed right text selection handle is not moved after left text selection handle is selected.
[Issue#] N_SE_37401
[Problem] Right text selection handle is not moved after left text selection handle is selected.
[Cause] Left text selection handle was selected and then,
        when right text selection handle is selected,
        isMouseDowned() value of both left and right handles is true.
        So, selected handle is alwyas left text selection handle due to below code.
          - "TextSelectionHandle* selectionHandle = m_leftHandle->isMouseDowned()? m_leftHandle : m_rightHandle;"
[Solution] Added m_selectedHandle variable and changed routine to get selected handle.

Change-Id: I5b6cbd38ff14de8a2747112622be9d2196f11eb5