[Feature request] Integrate with Test Explorer

There is a [Test Explorer UI extension](https://marketplace.visualstudio.com/items?itemName=hbenl.vscode-test-explorer) available, which itself provides a [Test Adapter API to discover and run tests](https://github.com/hbenl/vscode-example-test-adapter). An example of such test adapter is the [Catch2 and GoogleTest adapter](https://marketplace.visualstudio.com/items?itemName=matepek.vscode-catch2-test-adapter).

It would be very neat if the vscode-bazel extension was integrating with either Test Explorer directly, or with the GoogleTest adapter, in order to provide the list of tests, and the ability to spawn a [Visual Studio Code Debugger instance](https://code.visualstudio.com/docs/cpp/cpp-debug) through the Test Explorer UI.

Start by reading the linked Test Explorer UI extension and Test Adapter API, then compare the Catch2 and GoogleTest adapter example with the vscode-bazel extension. Done means exposing Bazel tests through Test Explorer and enabling a Visual Studio Code Debugger instance from the Test Explorer UI.

Written by the indexing model from the issue text.