Input variables in tasks

[alexr00]

Fixes #4758

[alexr00]

@isidorn, could you take a look at the configurationResolver* files? I made some significant changes to them and I want to make sure you're ok with them.

[isidorn]

@alexr00 I took a look at the changes you made to the configuratoinResolver files and they look good to me overall. Great job! I also see you added some tests, so I would just verify:

• all the tests are green -> this seems to be good
• variables still get resolved for all the cases
  • ${workspaceRoot}
  • ${env:PATH}
  • ${command:SOME_COMMAND}
  • ${config:editor.lineHeight}

Apart from that I would add a bit more comments once you find the time. I know it was like that before, but we could improve this.
Added some minor comments inline. I can do a more thourugh review in a couple of days when I have more time.

@weinand might also want to take a look at the changes.

[weinand]

@alexr00 Please make sure that variables are resolved correctly in all builds