Refactor: Move geometry nodes execute implementation for reusability

For node group operators (#101778), it helps to reuse the existing
geometry nodes execution. This commit adds a new moves most
of the geometry computation to the nodes module and gives the
modifier (and in the future the operator) a callback to setup the
execution context.

@@ -0,0 +61,4 @@
+std::unique_ptr<IDProperty, bke::idprop::IDPropertyDeleter> id_property_create_from_socket(
+    const bNodeSocket &socket);
+
+GeometrySet execute_geometry_nodes(const bNodeTree &btree,

@@ -0,0 +3,4 @@
+#pragma once
+
+/**
+ * For evaluation, geometry node groups are converted to a lazy-function graph. The generated graph