Load project to hold ruleset compilation options

[savpek]

Resolves one review issue from original PR #1076 / first two bullets from #1301 and #1458.

This version loads rulesets as part of project instead of joining them to project on every analysis routine.

End user gets:

• Dynamically loaded / modifiable rulesets instead without full restart on omnisharp after every change.
• Reanalyze updated projects.
• CS0000 diagnostics can be controlled by rulesets even when analyzers are not enabled.
• (Very) slightly faster analysis since project isn't updated every time.
• When project is restored -> it is re-analyzed with correct depencies.

Pending

• Tests (fix existing + add new that tests for project loader).
• Tweaks

[savpek]

@rchande @filipw @mholo65 @david-driscoll ready for review.

[filipw]

Marking as blocked until #1474 (so that this one goes first).

[savpek]

Ready for re-review @rchande @filipw

Current behavior:

[filipw]

LGTM

[filipw]

@savpek if you don't mind, it should be squashed on merge

[savpek]

@savpek if you don't mind, it should be squashed on merge

Squashing is fine 🙂

[filipw]

@rchande @david-driscoll @mholo65 could you guys please have a look? imho should be good to go

[bjorkstromm]

Looks good to me. My comments are just nitpicking.

Looks like the changes have been addressed

[david-driscoll]

Looks good to me, looks like @rchande changes have been addressed as well. Going to update the branch to ensure there are no conflicts.

[filipw]

thanks!

[filipw]

Squashing is fine 🙂

forgot to do it 😄