Add missing button actions (#119)

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## Description
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Allow L or Z to be used in the menu.
For instance, could be used to show extra info in the `ROM Info`
display.

## Motivation and Context
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issue here -->
These buttons were not available.

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## Types of changes
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- [x] Improvement (non-breaking change that adds a new feature)
- [ ] Bug fix (fixes an issue)
- [ ] Breaking change (breaking change)
- [ ] Config and build (change in the configuration and build system,
has no impact on code or features)

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- [ ] All new and existing tests passed.

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src/menu/actions.c

@@ -21,6 +21,8 @@ static void actions_clear (menu_t *menu) {
     menu->actions.back = false;
     menu->actions.options = false;
     menu->actions.settings = false;
+    menu->actions.l_context = false;
+    menu->actions.z_context = false;
 }
 
 static void actions_update_direction (menu_t *menu) {
@@ -91,6 +93,10 @@ static void actions_update_buttons (menu_t *menu) {
         menu->actions.options = true;
     } else if (pressed.start) {
         menu->actions.settings = true;
+    } else if (pressed.l) {
+        menu->actions.l_context = true;
+    }  else if (pressed.z) {
+        menu->actions.z_context = true;
     }
 }
 

src/menu/menu_state.h

@@ -85,6 +85,8 @@ typedef struct {
         bool back;
         bool options;
         bool settings;
+        bool l_context;
+        bool z_context;
     } actions;
 
     struct {