Add schema validation for collection files #369

This commit improves collection file editing and error detection
directly in the IDE. It adds YAML schema, IDE configuration and
automatic tests to validate it.

- Introduce a YAML schema for collection file.
- Use `yaml-language-server` for enhanced YAML support in VSCode.
- Add telemetry disabling in `configure_vscode.py` to respect user
  privacy.
- Add automated checks to validate YAML file structure against the
  schema.
- Remove unused properties and do not allow them in compiler.

.vscode/extensions.json

@@ -5,8 +5,10 @@
     "wengerk.highlight-bad-chars",      // Highlights bad chars.
     "wayou.vscode-todo-highlight",      // Highlights TODO.
     "wix.vscode-import-cost",           // Shows in KB how much a require include in code.
-    // Documentation
+    // Markdown
     "davidanson.vscode-markdownlint",   // Lints markdown.
+    // YAML
+    "redhat.vscode-yaml",               // Lints YAML files, validates against schema.
     // TypeScript / JavaScript
     "dbaeumer.vscode-eslint",           // Lints JavaScript/TypeScript.
     "pmneo.tsimporter",                 // Provides better auto-complete for TypeScripts imports.