[TextEditor] Fix wrong invalidation of LayoutDescriptor and ChunkDescriptor

Actual fix in this commit is YToLine instead of textEditor.GetTextEditorData ().VAdjustment.Value / LineHeight which didn't take folded text into calculation resulting in miscalculating startLine/endLine for number of folded lines before current line. So it was invalidating LayoutDescriptor and ChunkDescriptor cache for all lines... hence performance hit on scrolling(mouse scroll, moving up or down with keyboard , debug stepping...)

I also moved linesToRemove into method since don't see good reason for being field... and small optimization for calculating startLine/endLine...