feat: add insert_after and insert_startup_before (#13941)

# Objective

Fixes #13866 

## Solution

Add `insert_before` in **FixedMainScheduleOrder** and
**MainScheduleOrder**, add `insert_startup_before` in
**MainScheduleOrder**, applying the same logic as `insert_after`, except
for parameters naming and insertion index.

crates/bevy_app/src/main_schedule.rs

@@ -195,6 +195,16 @@ impl MainScheduleOrder {
  self.labels.insert(index + 1, schedule.intern());
  }
 
+ /// Adds the given `schedule` before the `before` schedule in the main list of schedules.
+ pub fn insert_before(&mut self, before: impl ScheduleLabel, schedule: impl ScheduleLabel) {
+ let index = self
+ .labels
+ .iter()
+ .position(|current| (**current).eq(&before))
+ .unwrap_or_else(|| panic!("Expected {before:?} to exist"));
+ self.labels.insert(index, schedule.intern());
+ }
+
  /// Adds the given `schedule` after the `after` schedule in the list of startup schedules.
  pub fn insert_startup_after(
  &mut self,
@@ -208,6 +218,20 @@ impl MainScheduleOrder {
  .unwrap_or_else(|| panic!("Expected {after:?} to exist"));
  self.startup_labels.insert(index + 1, schedule.intern());
  }
+
+ /// Adds the given `schedule` before the `before` schedule in the list of startup schedules.
+ pub fn insert_startup_before(
+ &mut self,
+ before: impl ScheduleLabel,
+ schedule: impl ScheduleLabel,
+ ) {
+ let index = self
+ .startup_labels
+ .iter()
+ .position(|current| (**current).eq(&before))
+ .unwrap_or_else(|| panic!("Expected {before:?} to exist"));
+ self.startup_labels.insert(index, schedule.intern());
+ }
 }
 
 impl Main {
@@ -291,6 +315,16 @@ impl FixedMainScheduleOrder {
  .unwrap_or_else(|| panic!("Expected {after:?} to exist"));
  self.labels.insert(index + 1, schedule.intern());
  }
+
+ /// Adds the given `schedule` before the `before` schedule
+ pub fn insert_before(&mut self, before: impl ScheduleLabel, schedule: impl ScheduleLabel) {
+ let index = self
+ .labels
+ .iter()
+ .position(|current| (**current).eq(&before))
+ .unwrap_or_else(|| panic!("Expected {before:?} to exist"));
+ self.labels.insert(index, schedule.intern());
+ }
 }
 
 impl FixedMain {