Add editor-agnostic dev container configuration for Shipilev Loom builds

[Copilot]

Eliminates manual Loom JDK setup by providing an editor-agnostic dev container using the same shipilev/openjdk:loom image as CI.

Changes

• .devcontainer/devcontainer.json: Editor-agnostic dev container configuration that matches CI environment

  • Uses shipilev/openjdk:loom Docker image
  • Installs Maven and Git on creation
  • Sets JAVA_HOME environment variable for universal IDE compatibility
  • Includes optional VS Code extensions and settings
  • Forwards port 8080 for example-echo server

• README.md: Added dev container setup instructions for multiple IDEs

  • Separate setup guides for VS Code and IntelliJ IDEA
  • 4-step setup for each IDE
  • Clear explanation of what the dev container provides
  • Existing manual JDK setup preserved as alternative

Developers can now start contributing using their preferred IDE (VS Code or IntelliJ IDEA) without downloading or building Loom JDK manually.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Support dev containers to ease developing locally with the Shipilev loom containers</issue_title>
<issue_description>#55 has introduced using the Shipilev container for loom: we should provide dev containers using the same image to ease developing locally without any need to build JDK/download any loom build.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Support dev containers to ease developing locally with the Shipilev loom containers #57

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[franz1981]

@copilot
Add info for IDEA as well

[franz1981]

@copilot make it VSCode agnostic please

[Copilot]

@copilot
Add info for IDEA as well

Added IntelliJ IDEA support in commit c90f56d. The README now includes step-by-step instructions for using the dev container with both VS Code and IntelliJ IDEA.

@copilot make it VSCode agnostic please

Made the configuration editor-agnostic in commit c90f56d. Core settings like JAVA_HOME are now set as container environment variables, and editor-specific customizations are clearly marked as optional at the bottom of the config.