Add CI tests for dynamic workspace files

[jonatanschroeder]

A recent change in ESM exports caused issues in dynamic workspace files that were only detected by unrelated manual testing. A CI test would likely have caught these errors more quickly and avoided this problem. The test should include:

• Static files in the workspace directory (for completeness);
• Files in workspaceTemplates, with or without mustache extension;
• Files linked from params;
• Files with content in params, including text and binary, in utf-8, base64 and hex;
• Blank files;
• Files in subdirectories.