Confusion about how EnvironmentVariableCollection handles multiple extensions changing the same variable

[mjbvz]

Refs #93601

Repro

1. In Extension 1, create a persisted EnvironmentVariableCollection that calls .replace('TEST', 'replace')

2. In extension 2, create a non persisted EnvironmentVariableCollection that calls .append('TEST', 'append')

3. Install both extensions

4. Activate extension 1.

5. Then restart VS Code

6. Now activate extension 2

7. Create a new terminal and check the value of TEST

Expected
I expected TEST to be replaceappend

This is because I expect the initial value of TEST to be replace from the persisted collection in extension 1, then when extension 2 is activated it appends on its value.

Actual
The value of TEST is replace

[Tyriar]

Discussed this in the API call, the order is reverse to what it's meant to be right now.