Add context menus to Variables view to auto show 'toString()' value

[testforstephen]

This partially mitigate the issue #1297.

• Remove the old menus "Enable/Disable 'toString()' Object View"
• Instead, add new context menus "Auto/Manual Expand Lazy Variables" to Variables view.
  • "Auto Expand Lazy Variables" will show the toString() value directly.
  • "Manual Expand Lazy Variables" then shows an eye icon on Object instance, and click it to expand toString value.