fix(46466): add missing async keyword before type parameters (#46467)

Author: a-tarasyuk

src/services/codefixes/fixAwaitInSyncFunction.ts

@@ -53,7 +53,8 @@ namespace ts.codefix {
                 insertBefore = findChildOfKind(containingFunction, SyntaxKind.FunctionKeyword, sourceFile);
                 break;
             case SyntaxKind.ArrowFunction:
-                insertBefore = findChildOfKind(containingFunction, SyntaxKind.OpenParenToken, sourceFile) || first(containingFunction.parameters);
+                const kind = containingFunction.typeParameters ? SyntaxKind.LessThanToken : SyntaxKind.OpenParenToken;
+                insertBefore = findChildOfKind(containingFunction, kind, sourceFile) || first(containingFunction.parameters);
                 break;
             default:
                 return;

tests/cases/fourslash/codeFixAddMissingAsync3.ts

@@ -0,0 +1,16 @@
+/// <reference path="fourslash.ts" />
+
+////const foo = <T>(x: T): string => {
+////    await new Promise(resolve => resolve(true));
+////    return "";
+////}
+
+verify.codeFix({
+    description: ts.Diagnostics.Add_async_modifier_to_containing_function.message,
+    index: 0,
+    newFileContent:
+`const foo = async <T>(x: T): Promise<string> => {
+    await new Promise(resolve => resolve(true));
+    return "";
+}`
+});