Support WSL for multi-line prompt clearing

src/vs/workbench/parts/terminal/electron-browser/terminalInstance.ts

@@ -567,7 +567,7 @@ export class TerminalInstance implements ITerminalInstance {
 	}
 
 	public clear(): void {
-		if (paths.basename(this._shellLaunchConfig.executable).match(/zsh|bash/)) {
+		if (this._shellLaunchConfig.executable && paths.basename(this._shellLaunchConfig.executable).match(/^(zsh|bash|bash\.exe)$/)) {
 			// If a supported shell is being used, clear xterm scrollback then clear shell (^L)
 			this._xterm.write('\x1b[3J');
 			this._processManager.write('\x0c');