Motivation for the change, related issues

Today, Playground enables Xdebug during boot which may be surprising to users. If the debugger breaks at the first line, the user will be debugging the Playground boot process. Let's skip this by default and consider adding a command line flag to enable boot-time Xdebug breaks.

Implementation details

A big change in this PR is that the first Playground worker is now only used during boot. We discard it after that boot and setup process completes. Some positive consequences of this change are:

• Reflects the truth that the Playground worker has special configuration and responsibilities as part of the boot process.
• Allows us to be clear that all post-boot workers are based on the same configuration and truth. There is no remaining special boot-time worker that might behave differently from the others.
• Allows us to control whether the boot-and-setup worker has Xdebug enabled separately from the regular workers.

Testing Instructions (or ideally a Blueprint)

Before checking out this branch:

• Create a local directory at the top level of your Playground working dir that can be mounted as /wordpress
• Run npx nx unbuilt-asyncify playground-cli -- server --mount-dir <local-dir> /wordpress so Playground will download and install WordPress in your local directory.
• Open the local directory as a project root in Visual Studio Code, select the debug pane, and create a launch.json file containing the following configuration:

  {
      "name": "PR test for WP Playground CLI - Listen for Xdebug",
      "type": "php",
      "request": "launch",
      "port": 9003,
      "pathMappings": {
          "/": "${workspaceFolder}/.playground-xdebug-root",
          "/wordpress": "${workspaceFolder}/"
      },
      "stopOnEntry": true,
  }
  

• Start the "PR test for WP Playground CLI - Listen for Xdebug" debug target within vscode
• cd into the local WP dir and run the following command and confirm that vscode hit a breakpoint before the "WordPress is running on https://127.0.0.1:9400" message is printed:
  node --experimental-strip-types --experimental-transform-types --disable-warning=ExperimentalWarning --import ../packages/meta/src/node-es-module-loader/register.mts ../packages/playground/cli/src/cli.ts server --auto-mount=. --verbosity=debug --skip-wordpress-setup --xdebug --experimental-unsafe-ide-integration --php=8.3 --experimental-multi-worker=4

After checking out this branch:

• Open the previously created local WP dir as the workspace root within vscode
• Run the "PR test for WP Playground CLI - Listen for Xdebug" debug target
• cd into the local WP dir, re-run the above node command, and confirm that no breakpoint was hit during the boot process.