Add forward class definition for std::filesystem::path class

The namespace is missing for the path class, so this provides
more type information to fix this problem.

Closes #2993

CHANGES.current

@@ -7,6 +7,9 @@ the issue number to the end of the URL: https://github.com/swig/swig/issues/
 Version 4.3.0 (in progress)
 ===========================
 
+2024-08-19: wsfulton
+	    [Python] #2993 Add missing std::filesystem namespace to std_filesystem.i.
+
 2024-08-17: olly
 	    #904 #1907 #2579 Fix string literal and character literal wrapping bugs.
 

Examples/test-suite/cpp17_std_filesystem.i

@@ -58,7 +58,8 @@ std::string pathPtrToStr(const std::filesystem::path * p) {
     return p->string();
 }
 
-std::filesystem::path roundTrip(const std::filesystem::path& p) {
+namespace stdfs = std::filesystem;
+std::filesystem::path roundTrip(const stdfs::path& p) {
     return p;
 }
 %}

Lib/python/std_filesystem.i

@@ -8,6 +8,12 @@
 #include <filesystem>
 %}
 
+namespace std {
+  namespace filesystem {
+    class path;
+  }
+}
+
 %fragment("SWIG_std_filesystem", "header") {
 SWIGINTERN PyObject *SWIG_std_filesystem_importPathClass() {
   PyObject *module = PyImport_ImportModule("pathlib");