Specify a name for a Property in a code example.

It is good practice to specify a name for the `testing::Property` matcher's use in diagnostics, and we should do so in our examples.

PiperOrigin-RevId: 496406309
Change-Id: Ibb4d1ba63771b5d6855442b91564027cda8ddaca

docs/gmock_cook_book.md

@@ -904,7 +904,7 @@ using ::testing::Contains;
 using ::testing::Property;
 
 inline constexpr auto HasFoo = [](const auto& f) {
-  return Property(&MyClass::foo, Contains(f));
+  return Property("foo", &MyClass::foo, Contains(f));
 };
 ...
   EXPECT_THAT(x, HasFoo("blah"));