ELECTRON_RUN_AS_NODE is inherited from the VSCode environment when building a CMake target

I have defined a custom CMake target to build our documentation using the Python tool Sphinx. As part of the documentation building process, drawio, an Electron based application, is executed and fails with the following error message: `drawio: bad option --export`. This only occurs when building the CMake target using the CMake Tools VSCode extension. There is no problem when running the target from a terminal, inside or outside of VSCode. Also invoking Sphinx from a VSCode launch/debug configuration is without issues.

I have found that the root cause for this is that Electron applications behave like this when the [ELECTRON_RUN_AS_NODE](https://www.electronjs.org/docs/api/environment-variables#electron_run_as_node) environment variable is set (see https://github.com/electron/electron/issues/18412). VSCode cleans the environment for its terminals and when starting debug sessions. I believe CMake Tools should do the same when building a target, [making sure it doesn't affect VSCode's environment](https://github.com/electron/electron/pull/19742).

### Platform and Versions

- **Operating System**: Ubuntu 18.04
- **CMake Version**: 3.17.4
- **VSCode Version**: 1.51.0
- **CMake Tools Extension Version**: 1.5.2

Start with the CMake Tools path that builds a custom CMake target, reproducing the Sphinx target that invokes drawio under the VSCode extension. Compare its environment with the terminal and launch/debug paths, focusing on ELECTRON_RUN_AS_NODE. Done means the target no longer inherits that variable while VSCode's environment remains unaffected.

Written by the indexing model from the issue text.