[core] remove virtual-widget and virtual-renderer

Fixes #2300

Both the `virtual-widget` and `virtual-renderer` have been deprecated
since #2301. This patch cleans
up the codebase to remove the deprecated code as it should no longer be used/supported.

- removes the deprecated `virtual-widget`.
- removes the deprecated `virtual-renderer`.

One should instead opt to use `react-widget` and `react-renderer`.

Signed-off-by: vince-fugnitto <vincent.fugnitto@ericsson.com>

CHANGELOG.md

@@ -4,6 +4,8 @@
 
 Breaking changes:
 
+- [core] removed `virtual-renderer`. `react-renderer` should be used instead [#6885](https://github.com/eclipse-theia/theia/pull/6885)
+- [core] removed `virtual-widget`. `react-widget` should be used instead [#6885](https://github.com/eclipse-theia/theia/pull/6885)
 - [task] renamed method `getStrigifiedTaskSchema()` has been renamed to `getStringifiedTaskSchema()` [#6780](https://github.com/eclipse-theia/theia/pull/6780)
 - [task] renamed method `reorgnizeTasks()` has been renamed to `reorganizeTasks()` [#6780](https://github.com/eclipse-theia/theia/pull/6780)
 - Support VS Code icon and color theming. [#6475](https://github.com/eclipse-theia/theia/pull/6475)
@@ -42,7 +44,7 @@ Breaking changes:
             });
         ```
       - or install from a VS Code extension.
-    - One should not introduce css color variables anymore or hardcode colors in css. 
+    - One should not introduce css color variables anymore or hardcode colors in css.
     - One can contribute new colors by implementing `ColorContribution` contribution point and calling `ColorRegistry.register`.
     It's important that new colors are derived from existing VS Code colors if one plans to allow installation of VS Code extension contributing color themes.
     Otherwise, there is no guarantee that new colors don't look alien for a random VS Code color theme.

packages/core/src/browser/widgets/index.ts

@@ -15,7 +15,5 @@
  ********************************************************************************/
 
 export * from './widget';
-export * from './virtual-renderer';
-export * from './virtual-widget';
 export * from './react-renderer';
 export * from './react-widget';