Don't scroll terminal to top when hidden and shown

Fixes microsoft#134692

Author: Tyriar

src/vs/workbench/contrib/terminal/browser/terminalInstance.ts

@@ -1171,13 +1171,13 @@ export class TerminalInstance extends Disposable implements ITerminalInstance {
 			// using cached dimensions of a split terminal).
 			this._resize();
 
-			// Trigger a manual scroll event which will sync the viewport and scroll bar. This is
+			// Trigger a forced refresh of the viewport to sync the viewport and scroll bar. This is
 			// necessary if the number of rows in the terminal has decreased while it was in the
 			// background since scrollTop changes take no effect but the terminal's position does
 			// change since the number of visible rows decreases.
 			// This can likely be removed after https://github.com/xtermjs/xterm.js/issues/291 is
 			// fixed upstream.
-			this._xtermCore._onScroll.fire(this._xterm.buffer.active.viewportY);
+			this._xtermCore.viewport._innerRefresh();
 		}
 	}
 

src/vs/workbench/contrib/terminal/browser/xterm-private.d.ts

@@ -3,12 +3,16 @@
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
 
+/* eslint-disable @typescript-eslint/naming-convention */
+
 import { IBufferCell } from 'xterm';
 
 export type XTermAttributes = Omit<IBufferCell, 'getWidth' | 'getChars' | 'getCode'> & { clone?(): XTermAttributes };
 
 export interface XTermCore {
-	_onScroll: IEventEmitter<number>;
+	viewport: {
+		_innerRefresh(): void;
+	};
 	_onKey: IEventEmitter<{ key: string }>;
 
 	_charSizeService: {