Lazily update frames of all threads in all-stop mode

[sfrylmark]

What it does

When a breakpoint occurs in a thread in all-stop mode, all other
threads have outdated/missing stackframes which means no variables
show up and can be inspected. This fixes the issue by marking each
thread as potentially having "dirty" frames: frames that need to be
re-fetched when the user selects them.

How to test

Testing is unfortunately quite complex at the moment. This is because @theia/cpp-debug is using an outdated version of a vscode extension. If you test these changes before and after, you'll see that before, you could only access the current thread's frames. After, you'll see that you can play around with all your frames as expected.

Step 1: Build the debugger vscode extension manually

The latest release of our fork is using an outdated adapter.

1. Clone https://github.com/theia-ide/cdt-gdb-vscode
2. Build the vscode extension yarn && yarn vsce:package
3. Launch a simple webserver serving this file.
   Python 2: python -m SimpleHTTPServer
   Python 3: python -m http.server

Step 2: Add the extension to theia

1. Add "cdt-gdb-vscode": "http://localhost:8000/cdt-gdb-vscode-0.0.90.vsix" to the root package.json under "theiaPlugins".
2. Make sure you don't have a plugins/cdt-gdb-vscode laying around.
3. yarn at the root, then yarn start:browser. If you've only updated the plugin, it's fine to just run yarn download:plugins instead of yarn.

Step 3: Get an example workspace

Debug a multi-threaded program with the GDB support, an example is https://github.com/zappala/pthreads-examples-c

1. Clone https://github.com/zappala/pthreads-examples-c
2. Compile with make -B CPPFLAGS=-ggdb
3. Add the following .theia/tasks.json:

{
  "version": "0.2.0",
  "configurations": [
    {
      "type": "gdb",
      "request": "launch",
      "name": "Example",
      "program": "${workspaceFolder}/example"
    }
  ]
}

Step 4: Play around with threads, both before and after this PR!

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

[paul-marechal]

I will try using the cdt-gdb-vscode extension directly, see how it goes.

[vince-fugnitto]

Closing for the moment, discussions will be taken offline in the meantime.

[akosyakov]

Please study VS Code code base for such changes as a reference implementation, don't invent here. We should align it.

[paul-marechal]

@akosyakov the changes look good to me. When you say "we should align [with vscode]", what would you see done differently here? VS Code doesn't use the same model classes as we do, so I see the current change as a minimal way to fix the issue with outdated frames.

[akosyakov]

VS Code doesn't use the same model classes as we do, so I see the current change as a minimal way to fix the issue with outdated frames

model is not but logic should be the same to respect DAP expectations and timing

[sfrylmark]

Bump?

[paul-marechal]

LGTM, @akosyakov @tsmaeder ?

[akosyakov]

@marechal-p let's try, it looks cleaner now, sorry i don't have headspace to think about implications right now or time to try it