add missing deprecated show overload

Add an old deprecated overload signature for OutputChannel.show in
theia.d.ts and update the implementation accordingly.

packages/plugin-ext/src/plugin/output-channel/output-channel-item.ts

@@ -52,8 +52,11 @@ export class OutputChannelImpl implements theia.OutputChannel {
         this.proxy.$clear(this.name);
     }
 
-    show(preserveFocus: boolean | undefined): void {
+    show(preserveFocusOrColumn?: boolean | theia.ViewColumn, preserveFocus?: boolean): void {
         this.validate();
+        if (typeof preserveFocusOrColumn === 'boolean') {
+            preserveFocus = preserveFocusOrColumn;
+        }
         this.proxy.$reveal(this.name, !!preserveFocus);
     }
 

packages/plugin/src/theia.d.ts

@@ -2782,6 +2782,16 @@ export module '@theia/plugin' {
          */
         clear(): void;
 
+        /**
+         * Reveal this channel in the UI.
+         *
+         * @deprecated Use the overload with just one parameter (`show(preserveFocus?: boolean): void`).
+         *
+         * @param column This argument is **deprecated** and will be ignored.
+         * @param preserveFocus When `true` the channel will not take focus.
+         */
+        show(column?: ViewColumn, preserveFocus?: boolean): void;
+
         /**
          * Reveal this channel in the UI.
          *