iOS: make unopt debug builds unopt and debug (#56226)

The following iOS builds were named "unopt" and "debug" but did not have
the `--unoptimized` flag passed to `gn`, resulting in them not being
unopt, and having the gn `is_debug` setting set to `false`:

* ios_debug_unopt_sim
* ios_debug_unopt_sim_arm64
* ios_debug_unopt_sim_arm64_extension_safe

No test changes because this is a compile config change.

Issue: flutter/flutter#156166

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

Author: cbracken

ci/builders/mac_unopt.json

@@ -241,6 +241,7 @@
                 "debug",
                 "--simulator",
                 "--no-lto",
+                "--unoptimized",
                 "--rbe",
                 "--no-goma",
                 "--xcode-symlinks",
@@ -367,6 +368,7 @@
                 "--runtime-mode",
                 "debug",
                 "--simulator",
+                "--unoptimized",
                 "--no-lto",
                 "--simulator-cpu",
                 "arm64",
@@ -435,6 +437,7 @@
                 "--runtime-mode",
                 "debug",
                 "--simulator",
+                "--unoptimized",
                 "--no-lto",
                 "--simulator-cpu",
                 "arm64",