Implement EnvironmentVariableMutatorOptions API.

[tsmaeder]

What it does

Implements options when mutating EnvironmentVariableCollections. Since Theia does not support shell integration scripts, one of the options is stubbed. See the related issue for details.

Fixes #12941

Contributed on behalf of STMicroelectronics

How to test

Install the attached extension. It exercises the various cases like so:

    context.environmentVariableCollection.append('MUTATED_DEFAULT', 'a string');
    context.environmentVariableCollection.append('MUTATED_TRUE', 'a string', { applyAtProcessCreation: true });
    context.environmentVariableCollection.append('MUTATED_FALSE', 'a string', { applyAtProcessCreation: false });
    context.environmentVariableCollection.append('MUTATED_INT_TRUE', 'a string', { applyAtShellIntegration: true, applyAtProcessCreation: false });

After startup, open a terminal. My expectation is that THE MUTATED_DEFAULT and MUTATED_TRUE are set in the terminal shell.

Follow-ups

If we ever decide to implement shell integration scripts, we need to honor the corresponding flag.

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[tsmaeder]

Here's the extension:

envvartest-0.0.1.zip

and here's the source:

envvartest.zip

[martin-fleck-at]

Thank you @tsmaeder! I checked the code with your extension and everything works as expected. Values are properly handled based on their mutator options, meaning that in our case if you have applyAtProcessCreation set to false explicitly, they will not be available and applyAtShellIntegration is only stubbed/ignored.