chore: Update cocoa examples to be easier to use (#13878)

## DESCRIBE YOUR PR

Improves the Apple examples so it can be copy pasted to generate the
first Sentry issue.

Fixes
[getsentry/sentry-cocoa#4991](getsentry/sentry-cocoa#4991)

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## PRE-MERGE CHECKLIST

*Make sure you've checked the following before merging your changes:*

- [x] Checked Vercel preview for correctness, including links
- [ ] PR was reviewed and approved by any necessary SMEs (subject matter
experts)
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team](https://github.com/orgs/getsentry/teams/docs)

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## EXTRA RESOURCES

- [Sentry Docs contributor guide](https://docs.sentry.io/contributing/)

Author: itaybre

platform-includes/capture-error/apple.mdx

@@ -3,8 +3,16 @@ You can capture errors with the `captureError` method. This method takes an `Err
 ```swift {tabTitle:Swift}
 import Sentry
 
+enum MyCustomError: Error {
+    case myFirstIssue
+}
+
+func thisFunctionThrows() throws {
+    throw MyCustomError.myFirstIssue
+} 
+
 do {
-    try aMethodThatMightFail()
+    try thisFunctionThrows()
 } catch {
     SentrySDK.capture(error: error)
 }
@@ -13,8 +21,18 @@ do {
 ```objc {tabTitle:Objective-C}
 @import Sentry;
 
+- (void)thisFunctionReturnsAnError:(NSError **)error {
+    *error = [NSError errorWithDomain:@"com.example.myapp"
+                                 code:1001
+                             userInfo:@{
+      NSLocalizedDescriptionKey: @"Something went wrong."
+    }];
+}
+
+// ... Your code
+
 NSError *error = nil;
-[self aMethodThatMightFail:&error]
+[self thisFunctionReturnsAnError:&error];
 
 if (error) {
     [SentrySDK captureError:error];