Add support for theia.DebugSession.parentSession

[tsmaeder]

What it does

Add suppport vor DebugSession.parentSession. Fixes eclipse-theia#11512

Adds support for the parentSession property in theia.d.ts. Includes some minor changes to make sure we're not sending theia.DebugSession object over the wire, but only session ids.

Contributed on behalf of ST Microelectronics

How to test

1. Install the vscode extension from here: https://github.com/tsmaeder/castletest (I've attached a pre-built copy to this issue).
2. Run Theia and open a copy of the theia source code
3. Run the "Run Browser Backend and Frontend" launch configuration
4. Select various debug sesssions and run the "Show active debug session" command from the command palette.
5. Observe: you should see the name of the correct parent session printed to the output of the Theia instance under test

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]

@planger how about a review?

[tsmaeder]

@sgraband this is an updated version of this PR: #53. I noticed a problem (debug session objects being sent over the wire) and did a better version. Could you have another look before I open a PR on the main Theia repo?

[planger]

Since @sgraband is looking at this change anyway, I think it makes more sense that he reviews this change rather than me.
Thanks @tsmaeder and @sgraband!

[sgraband]

Install the vscode extension from here: https://github.com/tsmaeder/castletest (I've attached a pre-built copy to this issue).

@tsmaeder I cannot see a pre-built copy of the extension on this PR or the issue. Am i not seeing something? 👀

[sgraband]

Thank you!

Apart from the missing pre built extension i mentioned above this looks and works great!

[tsmaeder]

I cannot see a pre-built copy of the extension on this PR or the issue. Am i not seeing something?

Promises, promises! Here you go:
castletest-0.0.1.zip

[sgraband]

Great! Thank you! I already tested it, as i still had the extension from my earlier review, but the theia main repo reviewer will probably not have it 😉

LGTM 👍