Automatically configure build environment when running xbuild #95

What is the problem or limitation you are having?

When running xbuild, it is necessary to "prepare" the environment - stripping the PATH for iOS, and injecting key variables for Android. This is cumbersome to do manually; there are a lot of required changes, and the paths required are often buried deep in support packages.

Describe the solution you'd like

Since xbuild manages the build process, and knows the location of support packages etc, it should automatically configure the build environment prior to invoking a build.

Describe alternatives you've considered

Status quo - require manual configuration of the environment for every build.

Additional context

No response