Add open configuration commands to Command Palette (VSCode)

[AdrianWilczynski]

Hi, this contributes Command Palette entries for opening Roslynator's configuration files: Roslynator: Open Configuration of Analyzers (roslynator.ruleset) and Roslynator: Open Configuration of Refactorings and Fixes (roslynator.config).

They create (if necessary - non-existent) configuration files and open them. In practice, they work like built-in Preferences: Open Settings (JSON) command.

You can call them by pressing Ctrl + Shift + P and typing their name.

This PR also moves omnisharp.json update out of the extension.ts file and bumps required VSCode version to be safe (I think I remember that recursive directory creation didn't work in VSCode a year ago, It works now and I'm just not sure when It was added; this PR can be made to work without this change though).

You can find tests for this functionality in openRoslynatorConfiguration.test.ts.

Let me know if this is something you'd be open to adding and if I should change/fix something before.

[josefpihrt]

Overally it looks fine.

Could you just change configurationFiles.ts to configurationFiles.generated.ts. In a future, I would like to create default content of ruleset and config file from one place.

[AdrianWilczynski]

Sure thing. I've changed it.