feat: Add option to switch behavior for "back to browser / home" in Reader activity (#2366)

## Summary

It would be nice to switch back to the file list from an Reader activity
via a short back button press. This change adds an Reader option to
switch the default behavior, so a short back button press in the Reader
activity can now go back to the file list, and a long press on back goes
back to the home view. This does a fair bit of refactoring, introducing
a new constant for the ms limit.

* **What changes are included?**

- Changes to the translation
- Additional global Reader option 
- Refactoring of the back button behavior in the Reader activity

src/activities/reader/ReaderUtils.h

@@ -6,10 +6,12 @@
 #include <Logging.h>
 
 #include "MappedInputManager.h"
+#include "activities/ActivityManager.h"
 
 namespace ReaderUtils {
 
 constexpr unsigned long GO_HOME_MS = 1000;
+constexpr unsigned long GO_BACK_OR_HOME_MS = GO_HOME_MS;
 constexpr unsigned long SKIP_HOLD_MS = 700;
 constexpr unsigned long BOOKMARK_HOLD_MS = 400;
 constexpr unsigned long BOOKMARK_MESSAGE_DURATION_MS = 2500;
@@ -96,4 +98,37 @@ void renderAntiAliased(GfxRenderer& renderer, RenderFn&& renderFn) {
   renderer.restoreBwBuffer();
 }
 
+struct BackNavCallback {
+  void* ctx;
+  void (*fn)(void*);
+};
+
+// Returns true if the back button was consumed (caller should return).
+// Long press (>= GO_BACK_OR_HOME_MS):
+// - default: go to file browser
+// - with backShortToFileBrowser: go home
+// Short press (< GO_BACK_OR_HOME_MS):
+// - default: go home
+// - with backShortToFileBrowser: go to file browser.
+inline bool handleBackNavigation(const MappedInputManager& mappedInput, ActivityManager& activityManager,
+                                 const char* filePath, BackNavCallback goHome) {
+  if (mappedInput.isPressed(MappedInputManager::Button::Back) && mappedInput.getHeldTime() >= GO_BACK_OR_HOME_MS) {
+    if (SETTINGS.backShortToFileBrowser) {
+      goHome.fn(goHome.ctx);
+    } else {
+      activityManager.goToFileBrowser(filePath);
+    }
+    return true;
+  }
+  if (mappedInput.wasReleased(MappedInputManager::Button::Back) && mappedInput.getHeldTime() < GO_BACK_OR_HOME_MS) {
+    if (SETTINGS.backShortToFileBrowser) {
+      activityManager.goToFileBrowser(filePath);
+    } else {
+      goHome.fn(goHome.ctx);
+    }
+    return true;
+  }
+  return false;
+}
+
 }  // namespace ReaderUtils