Add environment variable NX_TASK_TARGET_PROJECT_ROOT

[kitsunekyo]

For a lot of config files (playwright, jest, ...) the value of the {projectRoot} token would be extremely helpful to have at runtime. NX already provides the environment variable NX_TASK_TARGET_PROJECT, which will return the name of the project, so providing NX_TASK_TARGET_PROJECT_ROOT would be a perfect addition to that.

Usecase:
To set the output file for some of my reporters my playwright preset needs to be aware of the project root of the task being run. I can use @nx/devkits workspaceRoot export but thats about it. To get the {projectRoot} I have to do a manual file lookup to find the nearest package.json or project.json, which I then use as projectRoot value within my playwright-preset.js file.

Having an environment variable with the value of the project root of the task being run would make this a million times simpler.