Parse DAP messages to match VS Code API

[dsseng]

What it does

Fixes #7470

How to test

Please see #7470 (comment)

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

[akosyakov]

@sh7dm One has to create a simple drop-in VS Code extension and check that it works in VS Code and then in Theia. Such extension gets attached to the issue for others to test. Otherwise it is not clear how one ensure correctness.

[dsseng]

@akosyakov I can't create one, but this extension uses this API: https://github.com/microsoft/vscode/blob/f20785db318ebc6a931108c5c504028a75f8d581/extensions/debug-server-ready/src/extension.ts#L209. Reviewers can try to run it.

[dsseng]

Maybe we should ask issue author about how the issue was found and test in using their extension?

[akosyakov]

@sh7dm If some extension is using it, that's also fine, then just write down how an extension should be used to confirm correctness. We will try that it does not work on master and compare to this branch.

[akosyakov]

fyi for PR guidances: https://github.com/eclipse-theia/theia/blob/master/doc/pull-requests.md#requesting-a-review

[dsseng]

@akosyakov I tested this with updated extension by @ishche .
VS Code insiders:

Theia at 1453157:

Theia at 4442eb5 (this PR):

[akosyakov]

tested, looks good, thank you!