…g VerticalDrawOffset to class functions

VerticalDrawOffset will be applyed to:
- CalculateLinesToRender function
- SearchHighlightsRenderer.RenderHighlights (OffsetTop param)
- CanvasDrawingSession.DrawTextLayout (Y param)
- invisibleCharactersRenderer.DrawTabsAndSpaces (singleLineHeight param)
Also:
- UpdateScrollOffset function will be added for handle control vertical scroll offset changing
- float VerticalDrawOffset variable (default value is 0)
- double TopScrollOffset and BottomScrollOffset variables

…p of cursor position formula

…yout (Y param)

…if ContentVerticalScrollOffset property changed

…rmula

…rmula

…set management easier

…ing; Make TopScrollOffset and BottomScrollOffset field public for get

Code refactor:
- Move offset calculating logic to local function

Fixed bug:
- When cursor located out of viewport local offset not applied to vertical scroll value