vtk: clean up / reduce code repetition (#107617)

vtk: clean up / reduce code repetition

This refactors the vtk expressions to use a generic base expression,
which is used for all 3 versions.

vtk 7.x no longer uses gcc 8, since the quirk of it not building with
gcc 9 seems to have been fixed.

This also makes the python bindings available for all 3 versions, and
fixes building them for vtk 8 by adding a patch.

pkgs/top-level/python-packages.nix

@@ -7746,8 +7746,17 @@ in {
 
   vsts-cd-manager = callPackage ../development/python-modules/vsts-cd-manager { };
 
-  vtk = toPythonModule (pkgs.vtk_7.override {
-    inherit (self) python;
+  vtk = self.vtk_7;
+  vtk_7 = toPythonModule (pkgs.vtk_7.override {
+    pythonInterpreter = python;
+    enablePython = true;
+  });
+  vtk_8 = toPythonModule (pkgs.vtk_8.override {
+    pythonInterpreter = python;
+    enablePython = true;
+  });
+  vtk_9 = toPythonModule (pkgs.vtk_9.override {
+    pythonInterpreter = python;
     enablePython = true;
   });