renderer: Mark latched buttons differently than locked

There are some hacks here in the form of an extra field "appears_locked_from", which can be used to hint that the user should see the button as locked. Without it, there's some confusion on user side regarding buttons that change states unprompted.

src/action.rs

@@ -32,6 +32,8 @@ pub enum Action {
         /// Whether key has a latched state
         /// that pops when another key is pressed.
         latches: bool,
+        /// Should take on *locked* appearance whenever latch comes back to those views.
+        looks_locked_from: Vec<View>,
     },
     /// Hold this modifier for as long as the button is pressed
     ApplyModifier(Modifier),
@@ -51,14 +53,24 @@ pub enum Action {
 impl Action {
     pub fn is_locked(&self, view_name: &str) -> bool {
         match self {
-            Action::LockView { lock, unlock: _, latches: _ } => lock == view_name,
+            Action::LockView { lock, unlock: _, latches: _, looks_locked_from: _ } => lock == view_name,
+            _ => false,
+        }
+    }
+    pub fn has_locked_appearance_from(&self, locked_view_name: &str) -> bool {
+        match self {
+            Action::LockView { lock: _, unlock: _, latches: _, looks_locked_from } => {
+                looks_locked_from.iter()
+                    .find(|view| locked_view_name == view.as_str())
+                    .is_some()
+            },
             _ => false,
         }
     }
     pub fn is_active(&self, view_name: &str) -> bool {
         match self {
             Action::SetView(view) => view == view_name,
-            Action::LockView { lock, unlock: _, latches: _ } => lock == view_name,
+            Action::LockView { lock, unlock: _, latches: _, looks_locked_from: _ } => lock == view_name,
             _ => false,
         }
     }