Prepare NavigationServer for process() and physics_process() split

Prepares the NavigationServer API for a split of its functionality between frame process() and stepped physics_process().

servers/navigation_server_2d.h

@@ -308,7 +308,8 @@ public:
 	/// The result of this process is needed by the physics server,
 	/// so this must be called in the main thread.
 	/// Note: This function is not thread safe.
-	virtual void process(real_t delta_time) = 0;
+	virtual void process(double p_delta_time) = 0;
+	virtual void physics_process(double p_delta_time) = 0;
 	virtual void init() = 0;
 	virtual void sync() = 0;
 	virtual void finish() = 0;

servers/navigation_server_2d_dummy.h

@@ -163,8 +163,8 @@ public:
 	void query_path(const Ref<NavigationPathQueryParameters2D> &p_query_parameters, Ref<NavigationPathQueryResult2D> p_query_result, const Callable &p_callback = Callable()) override {}
 
 	void set_active(bool p_active) override {}
-
-	void process(real_t delta_time) override {}
+	void process(double p_delta_time) override {}
+	void physics_process(double p_delta_time) override {}
 	void init() override {}
 	void sync() override {}
 	void finish() override {}

servers/navigation_server_3d.h

@@ -346,7 +346,8 @@ public:
 	/// The result of this process is needed by the physics server,
 	/// so this must be called in the main thread.
 	/// Note: This function is not thread safe.
-	virtual void process(real_t delta_time) = 0;
+	virtual void process(double p_delta_time) = 0;
+	virtual void physics_process(double p_delta_time) = 0;
 	virtual void init() = 0;
 	virtual void sync() = 0;
 	virtual void finish() = 0;

servers/navigation_server_3d_dummy.h

@@ -196,7 +196,8 @@ public:
 
 	void free(RID p_object) override {}
 	void set_active(bool p_active) override {}
-	void process(real_t delta_time) override {}
+	void process(double p_delta_time) override {}
+	void physics_process(double p_delta_time) override {}
 	void init() override {}
 	void sync() override {}
 	void finish() override {}