[ADT] Use adl_being/end in map_range (#130508)

This is to make sure that ADT helpers consistently use argument
dependent lookup when dealing with input ranges.

This was a part of #87936 but reverted due to buildbot failures.

Also add `map_range` unit tests -- there were no pre-existing tests
AFAICT.

Author: kuhar

llvm/include/llvm/ADT/STLExtras.h

@@ -376,8 +376,7 @@ inline mapped_iterator<ItTy, FuncTy> map_iterator(ItTy I, FuncTy F) {
 
 template <class ContainerTy, class FuncTy>
 auto map_range(ContainerTy &&C, FuncTy F) {
-  return make_range(map_iterator(std::begin(C), F),
-                    map_iterator(std::end(C), F));
+  return make_range(map_iterator(adl_begin(C), F), map_iterator(adl_end(C), F));
 }
 
 /// A base type of mapped iterator, that is useful for building derived

llvm/unittests/ADT/STLExtrasTest.cpp

@@ -750,6 +750,18 @@ TEST(STLExtrasTest, DropEndDefaultTest) {
   EXPECT_EQ(i, 4);
 }
 
+TEST(STLExtrasTest, MapRangeTest) {
+  SmallVector<int, 5> Vec{0, 1, 2};
+  EXPECT_THAT(map_range(Vec, [](int V) { return V + 1; }),
+              ElementsAre(1, 2, 3));
+
+  // Make sure that we use the `begin`/`end` functions
+  // from `some_namespace`, using ADL.
+  some_namespace::some_struct S;
+  S.data = {3, 4, 5};
+  EXPECT_THAT(map_range(S, [](int V) { return V * 2; }), ElementsAre(6, 8, 10));
+}
+
 TEST(STLExtrasTest, EarlyIncrementTest) {
   std::list<int> L = {1, 2, 3, 4};