Fixes #186: TextBox.Text property assignment types only part of text.

Added Thread.Sleep(10) after each SendInput() call to release timeslice and allow target thread to process the input. Due to priority boost from user input it should pass execution to target thread correctly.
Fixes possible COMException during Window.WaitForProcess() execution.

If process exited already, then automationElement.Current.ProcessId throws COMException with E_FAIL. Hence, instead of getting processId every time, we'll take everything we need at ctor time and just use it afterwards.
Replaced usage of UIItem.Pattern(...) with extension method GetPattern<TPattern>()
Fixed issues with WPF ComboBox in UIA v3.
Partial solution for WinForms ComboBox.

For some reason, in UIA v3 ComboBox doesn't expose ExpandCollapsePattern. Instead it has button "Open" which can be clicked. This change abstracts required changes away.