Add environmentVariableCollection to PluginContext

[vinokurig]

What it does

Add environmentVariableCollection to PluginContext to align it with ExtensionContext from vscode.

related CQ: https://dev.eclipse.org/ipzilla/show_bug.cgi?id=22598
fixes #8405

How to test

1. Clone the test plugin and compile it, or download the vsix file
2. Start the plugin and run F1 => Environment variable: Open terminal. This command opens a new terminal with predefined environment variables and changes them with the help of the environmentVariableCollection plugin API:

        collection = context.environmentVariableCollection;
        collection.replace('A', '~a2~');
        collection.append('B', '~b2~');
        collection.prepend('C', '~c2~');

        const terminal = theia.window.createTerminal({
            env: {
                A: 'a1',
                B: 'b1',
                C: 'c1'
            }
        });
        terminal.show();
        terminal.sendText('echo $A');
        terminal.sendText('echo $B');
        terminal.sendText('echo $C');

See :

echo $A
echo $B
echo $C
[ivinokur@localhost environment-variable]$ echo $A
~a2~
[ivinokur@localhost environment-variable]$ echo $B
b1~b2~
[ivinokur@localhost environment-variable]$ echo $C
~c2~c1
[ivinokur@localhost environment-variable]$ 

3. The environment variable collection is stored by default, to test it stop the plugin and then start it again, open a new terminal and type echo $A $B $C, see:

~a2~ ~b2~ ~c2~

4. Run F1 => Environment variable: Clear collection, open a new terminal and type echo $A $B $C: see an empty line.

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

[azatsarynnyy]

Works well. Thank you for providing the test plugin!

[vinokurig]

@akosyakov @westbury Could you please take a look?

[benoitf]

Tested with prebuilt vsix

set of env variables and clear of env variables are propagated

I've also reworked sample to make it vs code compliant and try it on VS Code and I have the same result (set and clear commands)

[benoitf]

I propose to merge this PR this afternoon if there is no objection as it's already there since more than 3 weeks