Feature/sqlcmd : Enable running scripts with SQLCMD variables - Part 1

[udeeshagautam]

This contains:

1. Changes to enable running of a script file containing (and defined) SQLCMD variables. This will evolve to enable getting arguments from outside the script in later changes.
2. Changes to switch on/off Intellisense with changing SQLCMD mode. We will make changes to better handle the specific SQLCMD Intellisense later.

[coveralls]

Coverage increased (+0.3%) to 76.759% when pulling 516c54c on feature/sqlcmd into ec09ad2 on master.

[pensivebrian]

[ranasaria]

        return Task.FromResult(true);

even though this is not your change I suggest changing returns of Task.FromResult(true) to Task.CompletedTask. The previous code was the best option before .Net 4.6. But from .Net 4.6 it is best to use this predefined constant.

Here is some discussion on this topic:
https://stackoverflow.com/questions/13127177/if-my-interface-must-return-task-what-is-the-best-way-to-have-a-no-operation-imp

---

Refers to: src/Microsoft.SqlTools.ServiceLayer/LanguageServices/LanguageService.cs:1758 in 26eca53. [](commit_id = 26eca53, deletion_comment = False)