Add Method GetAllSelectedOptions to Select.MultipleSelect

[peterdresslar]

Rather than returning List as in GetAllSelectedValues() this method would return List. This would enable much easier programmatic access to adding a Selected Option to the Select.

[crevete]

I'm not sure I understand what we want exactly. In your fix, you just add a private method. Why private? If you just want to add a method to get all select options, I could add this in an another PR. Please let me know what you want exactly.