fix: Add .asmdef for editor scripts to resolve Mac build error

This commit introduces `Firebase.Editor.App.asmdef` in the `editor/app/src/` directory.

The purpose of this assembly definition file is to:
1. Define a distinct assembly named `Firebase.Editor.App` for the editor scripts located in `editor/app/src/` (including `DllLocationPatcher.cs`, `AnalyticsPlayModeSetup.cs`, and `FirebaseAnalyticsEditorConstants.cs`).
2. Ensure this assembly is compiled exclusively for the Unity Editor environment by setting `includePlatforms: ["Editor"]`.
3. Improve code organization and compilation consistency across different operating systems.

This change directly addresses a build error reported on Mac (`CS0103: The name 'FirebaseAnalyticsEditorConstants' does not exist in the current context`), which occurred because the editor scripts were not being compiled into a clearly defined assembly, leading to symbol resolution issues on that platform.

The new .asmdef file ensures that all relevant editor scripts are compiled together, making `FirebaseAnalyticsEditorConstants` accessible to other scripts within the same `Firebase.Editor.App` assembly during editor script compilation on all platforms.

Author: google-labs-jules[bot]

editor/app/src/Firebase.Editor.App.asmdef

@@ -0,0 +1,16 @@
+{
+    "name": "Firebase.Editor.App",
+    "rootNamespace": "Firebase.Editor",
+    "references": [],
+    "includePlatforms": [
+        "Editor"
+    ],
+    "excludePlatforms": [],
+    "allowUnsafeCode": false,
+    "overrideReferences": false,
+    "precompiledReferences": [],
+    "autoReferenced": true,
+    "defineConstraints": [],
+    "versionDefines": [],
+    "noEngineReferences": false
+}