Remove sync fs use in tasks

Fixes #70577

src/vs/base/node/processes.ts

@@ -5,6 +5,7 @@
 
 import * as path from 'vs/base/common/path';
 import * as fs from 'fs';
+import { promisify } from 'util';
 import * as cp from 'child_process';
 import * as nls from 'vs/nls';
 import * as Types from 'vs/base/common/types';
@@ -404,7 +405,7 @@ export function createQueuedSender(childProcess: cp.ChildProcess): IQueuedSender
 }
 
 export namespace win32 {
-	export function findExecutable(command: string, cwd?: string, paths?: string[]): string {
+	export async function findExecutable(command: string, cwd?: string, paths?: string[]): Promise<string> {
 		// If we have an absolute path then we take it.
 		if (path.isAbsolute(command)) {
 			return command;
@@ -435,15 +436,15 @@ export namespace win32 {
 			} else {
 				fullPath = path.join(cwd, pathEntry, command);
 			}
-			if (fs.existsSync(fullPath)) {
+			if (await promisify(fs.exists)(fullPath)) {
 				return fullPath;
 			}
 			let withExtension = fullPath + '.com';
-			if (fs.existsSync(withExtension)) {
+			if (await promisify(fs.exists)(withExtension)) {
 				return withExtension;
 			}
 			withExtension = fullPath + '.exe';
-			if (fs.existsSync(withExtension)) {
+			if (await promisify(fs.exists)(withExtension)) {
 				return withExtension;
 			}
 		}

src/vs/workbench/api/node/extHostTask.ts

@@ -712,7 +712,7 @@ export class ExtHostTask implements ExtHostTaskShape {
 					paths[i] = resolver.resolve(ws, paths[i]);
 				}
 			}
-			result.process = win32.findExecutable(
+			result.process = await win32.findExecutable(
 				resolver.resolve(ws, toResolve.process.name),
 				toResolve.process.cwd !== undefined ? resolver.resolve(ws, toResolve.process.cwd) : undefined,
 				paths

src/vs/workbench/contrib/tasks/electron-browser/terminalTaskSystem.ts

@@ -429,12 +429,12 @@ export class TerminalTaskSystem implements ITaskSystem {
 			variables.forEach(variable => variablesArray.push(variable));
 
 			return new Promise((resolve, reject) => {
-				this.configurationResolverService.resolveWithInteraction(workspaceFolder, variablesArray, 'tasks').then(resolvedVariablesMap => {
+				this.configurationResolverService.resolveWithInteraction(workspaceFolder, variablesArray, 'tasks').then(async resolvedVariablesMap => {
 					if (resolvedVariablesMap) {
 						if (isProcess) {
 							let processVarValue: string;
 							if (Platform.isWindows) {
-								processVarValue = win32.findExecutable(
+								processVarValue = await win32.findExecutable(
 									this.configurationResolverService.resolve(workspaceFolder, CommandString.value(task.command.name!)),
 									cwd ? this.configurationResolverService.resolve(workspaceFolder, cwd) : undefined,
 									envPath ? envPath.split(path.delimiter).map(p => this.configurationResolverService.resolve(workspaceFolder, p)) : undefined