to support this, I added a way to set different default value per language

changed meaning of closed file diagnostic option. now it is solely for performance. when the option is off, we will only do very minimum work for diagnostics for smal scope such as opened files.

Several options in the Features layer were still defined as static fields attributed with ExportOption, which is located in Workspaces.Desktop. Portable MEF does not support static fields for exports so it's necessary to implement IOptionsProviders for each set of options.

     Background:

     As discussed in the dev team all hands all code under the GitHub dotnet foundation is using a single process for contribution, API review, infrastructure and coding style. The idea is to present a unified view to our customer and give them a single story for contributing to any project under the dotnet foundation.

     https://github.com/dotnet/corefx/wiki/Contributing#c-coding-style

     The coding style transition is automated using a Roslyn based rewrite tool:

     https://github.com/dotnet/codeformatter

     This will be applied in stages across our developer tree. Right now the focus is on the Open directory as this is what is being presented on github. Code owners will be contacted before the transition happens.

     Note: this is a soft style requirement. There are no build errors that come from this change.
 (changeset 1408227)