Add getter for SystemMeta::last_run field. (#22516)

# Objective

Add `SytemMeta::get_last_run`.

Full description in issue:
#22487

## Solution

I added the getter. Since `Tick` is `Copy`, I just returned it by value.
Pretty simple.

## Testing

implemented for:
https://github.com/stinkytoe/shieldtank/blob/04d216a8db91749c9975c2756dc1a987e80b8aea/src/query/by_iid.rs#L117

example usages:
-
https://github.com/stinkytoe/axe_man_adventure/blob/77f070add41f99cef92f9db9e5e6269339476911/src/main.rs#L426
-
https://github.com/stinkytoe/dungeon_of_madness/blob/3ec5db4fe7b0b942e3dcd2037814a8717506bbc3/src/main.rs#L200

Co-authored-by: Alice Cecile <[email protected]>

Author: stinkytoe

crates/bevy_ecs/src/system/function_system.rs

@@ -110,6 +110,11 @@ impl SystemMeta {
     pub fn set_exclusive(&mut self) {
         self.flags |= SystemStateFlags::EXCLUSIVE;
     }
+
+    /// Expose a read only copy of `last_run`.
+    pub fn get_last_run(&self) -> Tick {
+        self.last_run
+    }
 }
 
 // TODO: Actually use this in FunctionSystem. We should probably only do this once Systems are constructed using a World reference