CMake: Build Target from tasks.json to support compound debugging

- I want to debug multiple individual executables together (server, client) that have no build time dependencies.
- I have `compounds` in `launch.json` that works for this.
- For each executable in my compound, I'd like to have `preLaunchTask` in `launch.json` to make sure those executables are rebuilt before debugging.
- In the preLaunchTasks I would like to be able to perform `CMake: Build Target`, so that I can build those targets.

There does not seem to be a way to perform `CMake: Build Target` from a task in `tasks.json`. Is there a way? Or does this need a new feature in CMake Tools? Thanks!

Start by tracing how the CMake: Build Target command is exposed and how tasks.json preLaunchTask entries interact with launch.json compounds. Confirm the expected behavior for rebuilding each executable before debugging, then validate it with a compound configuration covering multiple targets.

Written by the indexing model from the issue text.