Added support for Populating OptionSets metadata from early bound

[Nianwei]

…embly

Changed how picklistattributemetadata is generated in optionset fields using enum type

Handle two situations of OptionSet properties: 1)added extra property for Enum in addtion to OptionSetValue, or 2) generated return Enum only, no OptionSetValue

[Nianwei]

Addressing Issue #445