Add instructions for GPU debugging in Xcode (#19915)

# Objective

- Using Xcode can be confusing to setup for rust projects.

# Solution

- Add instructions to docs/profiling.md for how to use start debugging a
bevy project with Xcode's GPU debugging/profiling tools.

Author: jf908

docs/profiling.md

@@ -10,6 +10,7 @@
   - [Perf flame graph](#perf-flame-graph)
 - [GPU runtime](#gpu-runtime)
   - [Vendor tools](#vendor-tools)
+    - [Xcode's Metal debugger](#xcodes-metal-debugger)
   - [Tracy RenderQueue](#tracy-renderqueue)
 - [Compile time](#compile-time)
 
@@ -147,6 +148,33 @@ For profiling GPU work, you should use the tool corresponding to your GPU's vend
 
 Note that while RenderDoc is a great debugging tool, it is _not_ a profiler, and should not be used for this purpose.
 
+#### Xcode's Metal debugger
+
+Follow the steps below to start GPU debugging on macOS. There is no need to create an Xcode project.
+
+1. In the menu bar click on Debug > Debug Executable…
+
+    ![Xcode's menu bar open to Debug > Debug Executable...](https://github.com/user-attachments/assets/efdc5037-0957-4227-b29d-9a789ba17a0a)
+
+2. Select your executable from your project’s target folder.
+3. The Scheme Editor will open. If your assets are not located next to your executable, you can go to the Arguments tab and set `BEVY_ASSET_ROOT` to the absolute path for your project (the parent of your assets folder). The rest of the defaults should be fine.
+
+    ![Xcode's Schema Editor opened to an environment variable configuration](https://github.com/user-attachments/assets/29cafb05-0c49-4777-8d41-8643812e8f6a)
+
+4. Click the play button in the top left and this should start your bevy app.
+
+    ![A cursor hovering over the play button in XCode](https://github.com/user-attachments/assets/859580e2-779b-4db8-8ea6-73cf4ef696c9)
+
+5. Go back to Xcode and click on the Metal icon in the bottom drawer and then Capture in the following the popup menu.
+
+    ![A cursor hovering over the Capture button in the Metal debugging popup menu](https://github.com/user-attachments/assets/c0ce1591-0a53-499b-bd1b-4d89538ea248)
+
+6. Start debugging and profiling!
+
+![Xcode open to the Performance tab in the Debug Navigator.](https://github.com/user-attachments/assets/52732391-9306-44a9-ae01-dcf4573f77ab)
+
+These instructions were created for Xcode 16.4.
+
 ### Tracy RenderQueue
 
 While it doesn't provide as much detail as vendor-specific tooling, Tracy can also be used to coarsely measure GPU performance.