Ability to set Msbuild properties for design time

[TheAngryByrd]

Adds ability to change the global properties we pass to design time loading.

MsBuildProps-object-config-2.mp4

(Don't worry about the extra commits, it's build off #1060, I'll rebase when that's merged)

[TheAngryByrd]

Hmm what kind of tests do you think would be worth writing for this?

• Check that we don't get a tooltip for something behind a #ifdef Release
• change configuration to Release
• see we get a tooltip

[baronfel]

We should take this as an escape hatch if nothing else. I think it could be helpful for configuration changes, but longer term we should do something more structured there instead. When we document it in Ionide it would be good to have inline examples for Configuration.