Provide some degree of compatibility for GetShownText in Python

This patch keeps the new API for GetShownText (argument order inverted), but also allows calling the member without parameters.

pcbnew/python/swig/fp_text.i

@@ -6,3 +6,25 @@
 #include <fp_textbox.h>
 %}
 
+%extend FP_TEXT
+{
+    %pythoncode
+    %{
+    # KiCad 6 API compatibility
+    def GetShownText(self):
+        r"""GetShownText(FP_TEXT self) -> wxString"""
+        return _pcbnew.FP_TEXT_GetShownText(self, True, 0)
+    %}
+}
+
+
+%extend FP_TEXTBOX
+{
+    %pythoncode
+    %{
+    # KiCad 6 API compatibility
+    def GetShownText(self):
+        r"""GetShownText(FP_TEXTBOX self) -> wxString"""
+        return _pcbnew.FP_TEXTBOX_GetShownText(self, True, 0)
+    %}
+}

pcbnew/python/swig/pcb_text.i

@@ -8,3 +8,38 @@
 #include <pcb_textbox.h>
 %}
 
+
+%extend EDA_TEXT
+{
+    %pythoncode
+    %{
+    # KiCad 6 API compatibility
+    def GetShownText(self):
+        r"""GetShownText(EDA_TEXT self) -> wxString"""
+        return _pcbnew.EDA_TEXT_GetShownText(self, True, 0)
+    %}
+}
+
+
+%extend PCB_TEXT
+{
+    %pythoncode
+    %{
+    # KiCad 6 API compatibility
+    def GetShownText(self):
+        r"""GetShownText(PCB_TEXT self) -> wxString"""
+        return _pcbnew.PCB_TEXT_GetShownText(self, True, 0)
+    %}
+}
+
+
+%extend PCB_TEXTBOX
+{
+    %pythoncode
+    %{
+    # KiCad 6 API compatibility
+    def GetShownText(self):
+        r"""GetShownText(PCB_TEXTBOX self) -> wxString"""
+        return _pcbnew.PCB_TEXTBOX_GetShownText(self, True, 0)
+    %}
+}