Make TypeErrors more informative when an optional header is missing

E.g. trying to convert a `list` to a `std::vector<int>` without
including <pybind11/stl.h> will now raise an error with a note that
suggests checking the headers.

The note is only appended if `std::` is found in the function
signature. This should only be the case when a header is missing.
E.g. when stl.h is included, the signature would contain `List[int]`
instead of `std::vector<int>` while using stl_bind.h would produce
something like `MyVector`. Similarly for `std::map`/`Dict`, `complex`,
`std::function`/`Callable`, etc.

There's a possibility for false positives, but it's pretty low.

tests/test_stl.py

@@ -179,3 +179,22 @@ def test_stl_pass_by_pointer(msg):
     """  # noqa: E501 line too long
 
     assert m.stl_pass_by_pointer([1, 2, 3]) == [1, 2, 3]
+
+
+def test_missing_header_message():
+    """Trying convert `list` to a `std::vector`, or vice versa, without including
+    <pybind11/stl.h> should result in a helpful suggestion in the error message"""
+    import pybind11_cross_module_tests as cm
+
+    expected_message = ("Did you forget to `#include <pybind11/stl.h>`? Or <pybind11/complex.h>,\n"
+                        "<pybind11/functional.h>, <pybind11/chrono.h>, etc. Some automatic\n"
+                        "conversions are optional and require extra headers to be included\n"
+                        "when compiling your pybind11 module.")
+
+    with pytest.raises(TypeError) as excinfo:
+        cm.missing_header_arg([1.0, 2.0, 3.0])
+    assert expected_message in str(excinfo.value)
+
+    with pytest.raises(TypeError) as excinfo:
+        cm.missing_header_return()
+    assert expected_message in str(excinfo.value)