add test for issue 10843

Author: Salasar

tests/baselines/reference/findIndex.js

@@ -0,0 +1,10 @@
+//// [findIndex.ts]
+
+[].findIndex(function(elem, i, arr) {
+    return true;
+});
+
+//// [findIndex.js]
+[].findIndex(function (elem, i, arr) {
+    return true;
+});

tests/baselines/reference/findIndex.symbols

@@ -0,0 +1,11 @@
+=== tests/cases/conformance/es6/arrayMethods/findIndex.ts ===
+
+[].findIndex(function(elem, i, arr) {
+>[].findIndex : Symbol(Array.findIndex, Decl(lib.es2015.core.d.ts, --, --))
+>findIndex : Symbol(Array.findIndex, Decl(lib.es2015.core.d.ts, --, --))
+>elem : Symbol(elem, Decl(findIndex.ts, 1, 22))
+>i : Symbol(i, Decl(findIndex.ts, 1, 27))
+>arr : Symbol(arr, Decl(findIndex.ts, 1, 30))
+
+    return true;
+});

tests/baselines/reference/findIndex.types

@@ -0,0 +1,16 @@
+=== tests/cases/conformance/es6/arrayMethods/findIndex.ts ===
+
+[].findIndex(function(elem, i, arr) {
+>[].findIndex(function(elem, i, arr) {    return true;}) : number
+>[].findIndex : (predicate: (value: any, index: number, obj: any[]) => boolean, thisArg?: any) => number
+>[] : undefined[]
+>findIndex : (predicate: (value: any, index: number, obj: any[]) => boolean, thisArg?: any) => number
+>function(elem, i, arr) {    return true;} : (elem: any, i: number, arr: any[]) => boolean
+>elem : any
+>i : number
+>arr : any[]
+
+    return true;
+>true : boolean
+
+});

tests/cases/conformance/es6/arrayMethods/findIndex.ts

@@ -0,0 +1,5 @@
+//@target: ES6
+
+[].findIndex(function(elem, i, arr) {
+    return true;
+});