cast: Qualify symbol usage in PYBIND11_TYPE_CASTER

Permits using macro outside of pybind11::detail

Author: EricCousineau-TRI

include/pybind11/cast.h

@@ -85,11 +85,15 @@ protected:
                                                                                                   \
 public:                                                                                           \
     static constexpr auto name = py_name;                                                         \
-    template <typename T_, enable_if_t<std::is_same<type, remove_cv_t<T_>>::value, int> = 0>      \
-    static handle cast(T_ *src, return_value_policy policy, handle parent) {                      \
+    template <typename T_,                                                                        \
+              ::pybind11::detail::enable_if_t<                                                    \
+                  std::is_same<type, ::pybind11::detail::remove_cv_t<T_>>::value,                 \
+                  int> = 0>                                                                       \
+    static ::pybind11::handle cast(                                                               \
+        T_ *src, ::pybind11::return_value_policy policy, ::pybind11::handle parent) {             \
         if (!src)                                                                                 \
             return none().release();                                                              \
-        if (policy == return_value_policy::take_ownership) {                                      \
+        if (policy == ::pybind11::return_value_policy::take_ownership) {                          \
             auto h = cast(std::move(*src), policy, parent);                                       \
             delete src;                                                                           \
             return h;                                                                             \
@@ -100,7 +104,7 @@ public:
     operator type &() { return value; }                /* NOLINT(bugprone-macro-parentheses) */   \
     operator type &&() && { return std::move(value); } /* NOLINT(bugprone-macro-parentheses) */   \
     template <typename T_>                                                                        \
-    using cast_op_type = pybind11::detail::movable_cast_op_type<T_>
+    using cast_op_type = ::pybind11::detail::movable_cast_op_type<T_>
 
 template <typename CharT>
 using is_std_char_type = any_of<std::is_same<CharT, char>, /* std::string */