visibility: Centralize keyboard panel visibility policy and handling

With the policy being disentangled from application, it becomes testable.
This prepares for moving the entire visibility mechanism to the new class and taking away more pieces of ServerContextService.
In addition, this is a good warmup before trying to implement sizing policy.

src/submission.rs

@@ -24,6 +24,7 @@ use ::imservice;
 use ::imservice::IMService;
 use ::keyboard::{ KeyCode, KeyStateId, Modifiers, PressType };
 use ::layout;
+use ::ui_manager::VisibilityManager;
 use ::util::vec_remove;
 use ::vkeyboard;
 use ::vkeyboard::VirtualKeyboard;
@@ -38,14 +39,11 @@ pub mod c {
     use std::os::raw::c_void;
 
     use ::imservice::c::InputMethod;
+    use ::util::c::Wrapped;
     use ::vkeyboard::c::ZwpVirtualKeyboardV1;
 
     // The following defined in C
 
-    /// ServerContextService*
-    #[repr(transparent)]
-    pub struct UIManager(*const c_void);
-
     /// EekboardContextService*
     #[repr(transparent)]
     pub struct StateManager(*const c_void);
@@ -55,12 +53,18 @@ pub mod c {
     fn submission_new(
         im: *mut InputMethod,
         vk: ZwpVirtualKeyboardV1,
-        state_manager: *const StateManager
+        state_manager: *const StateManager,
+        visibility_manager: Wrapped<VisibilityManager>,
     ) -> *mut Submission {
         let imservice = if im.is_null() {
             None
         } else {
-            Some(IMService::new(im, state_manager))
+            let visibility_manager = visibility_manager.clone_ref();
+            Some(IMService::new(
+                im,
+                state_manager,
+                Box::new(move |active| visibility_manager.borrow_mut().set_im_active(active)),
+            ))
         };
         // TODO: add vkeyboard too
         Box::<Submission>::into_raw(Box::new(
@@ -75,23 +79,6 @@ pub mod c {
         ))
     }
 
-    /// Use to initialize the UI reference
-    #[no_mangle]
-    pub extern "C"
-    fn submission_set_ui(submission: *mut Submission, ui_manager: *const UIManager) {
-        if submission.is_null() {
-            panic!("Null submission pointer");
-        }
-        let submission: &mut Submission = unsafe { &mut *submission };
-        if let Some(ref mut imservice) = &mut submission.imservice {
-            imservice.set_ui_manager(if ui_manager.is_null() {
-                None
-            } else {
-                Some(ui_manager)
-            })
-        };
-    }
-
     #[no_mangle]
     pub extern "C"
     fn submission_use_layout(