Pin tabs similar to Visual Studio

[teintinu]

• IEditorInput.pinned from boolean to export enum Pinned {NO, SOFT, HARD} . NO = preview, SOFT is the current vscode pinned, and HARD is pin similar to Visual Studio
• CloseAllButPinned action and methods that close all editor where pinned !== HARD
• DblClick in title pin hard
• replaced CloseAllEditors by CloseAllButPinned in hotkey and explorerviewlet
• TODO:
  • Fix the terminology to clarify and one just one term for each concept
    • NO/PREVIEW
    • SOFT/KEEPOPEN
    • HARD/PINNED
  • Unpin
  • better UI
  • remember pinned tabs on vscode restart
  • more tests (just one test with HARD pin included)

I suggest new PRs for TODO's to avoid mergeconflicts

refers to #12622

[mention-bot]

@thr0w, thanks for your PR! By analyzing the history of the files in this pull request, we identified @bpasero and @egamma to be potential reviewers.

[msftclas]

@thr0w,
Thanks for having already signed the Contribution License Agreement. Your agreement was validated by Microsoft. We will now review your pull request.
Thanks,
Microsoft Pull Request Bot

[bpasero]

Closing due to inactivity.