Enables by default propperty panel

[netonjm]

This branch will enable by default native property panel. Right now this will be used only in monodevelop with our basic types (designers will a secondary approach to allow reflection types).

=================== CURRENT STATUS ======================

Detected issues in implementation:

• Values are not correctly persisted in StandardValues and Enums (combo box) (memery) and some are missing when properties are generated, it seems sometimes we are showing the values of the parent element (needs investigation)
  https://devdiv.visualstudio.com/DevDiv/_workitems/edit/959084
• Sometimes store values fails in StandardValues and Enums (maybe related to previous issue
  https://devdiv.visualstudio.com/DevDiv/_workitems/edit/959086
• Use NSPopupItem instead combobox for selection
• Some StandardValues doesn't show a combo in case of no items
• Property changes are stores in memory but not in files
• Cannot reset default value correctly
• Issue storing in double, float, flag and filepath
• Focus on another windows when editing a property makes proppy to clean all the results
  https://devdiv.visualstudio.com/DevDiv/_workitems/edit/999288

Proppy detected issues

• Remove first empty item from NSPopupItem
  
  [Mac] PredefinedValues adds an empty element on TValue string xamarin/Xamarin.PropertyEditing#646

• Include a mechanism to include separators in PredefinedValues
  Include a mechanism to include separators in PredefinedValues xamarin/Xamarin.PropertyEditing#644

• TabKeyLoop navigation seems to be broken in some views
  [Accessibility][Mac] TabKeyLoop navigation seems to be broken xamarin/Xamarin.PropertyEditing#643

=================== HOW TO TEST ======================**

• Create an extension with some Mock editors to test

https://gofile.io/?c=YFNPNh

Installing this Extension adds a new section of properties in every node in the Solution Pad

This are all the Editors we added in this PR and how are represented

1. String -> TextField
2. Bool -> Checkbox
3. Int - > TextField (only allows Int values)
4. Float -> TextField (only allows Float values)
5. TimeSpan -> TextField (only allows TimeSpan values)
6. Char -> TextField (only allows a Char value)
7. DateTime -> TextField (only allows a DateTime value)
8. Flags -> a table of CheckBoxes
9. StandardValues -> ComboBox
10. Enum -> ComboBox
11. FilePath -> Clickeable Label which allows select a new directory
12. Table -> Not implemented**
    Mac Collection Editor xamarin/Xamarin.PropertyEditing#117

Check Ide.log for changes details

Fixes VSTS #563555
Fixes VSTS #959084
Fixes VSTS #959086