Revert "preferences: fix PreferenceProvider.merge method (#12126)" (#12213)

This reverts commit b28c8b9.

Author: vince-fugnitto

examples/api-tests/src/launch-preferences.spec.js

@@ -25,7 +25,7 @@
  * Expectations should be tested and aligned against VS Code.
  * See https://github.com/akosyakov/vscode-launch/blob/master/src/test/extension.test.ts
  */
-describe.skip('Launch Preferences', function () {
+describe('Launch Preferences', function () {
     this.timeout(10_000);
 
     const { assert } = chai;

packages/core/src/browser/preferences/preference-provider.spec.ts

@@ -235,9 +235,6 @@ export abstract class PreferenceProvider implements Disposable {
                 if (JSONExt.isObject(source[key]) && JSONExt.isObject(value)) {
                     this.merge(source[key], value);
                     continue;
-                } else if (JSONExt.isArray(source[key]) && JSONExt.isArray(value)) {
-                    source[key] = [...JSONExt.deepCopy(source[key] as any), ...JSONExt.deepCopy(value)];
-                    continue;
                 }
             }
             source[key] = JSONExt.deepCopy(value);