Populate environment variables with information for launched apps

[hakasapl]

Is your feature request related to a problem? Please describe.
No

Describe the solution you'd like
For every process forked from MO2 via the executables, it would be great if environment variables could be set for that process that expose:

• Instance directory

These other things would be helpful but can be found from just the instance directory alone

• Game directory
• Base directory
• Profile directory
• Mod directory
• Download directory

Describe alternatives you've considered
Currently launched apps need to ask the user for their instance directory, which can cause issues if they pass the wrong one.

Additional context
Primarily interested for ParallaxGen which uses some of this information to determine from which mod each file comes from, and it doesn't make sense for this to be an MO2 extension because it does a lot more.