Here's a summary of the changes I've made to add SetDefaultEventParameters and ClearDefaultEventParameters to Analytics:

This change introduces two new C++ Analytics SDK functions:
- `SetDefaultEventParameters(const std::map<std::string, firebase::Variant>& params)`:
  This allows you to set default parameters (string, int64, double, bool, null)
  that will be included in all subsequent `LogEvent` calls.
  If a `firebase::Variant::Null()` is provided for a key, that specific
  default parameter will be cleared. Aggregate types (maps, vectors) are not
  supported and will be skipped with an error logged.
- `ClearDefaultEventParameters()`: This clears all currently set default event
  parameters.

Here's how it's handled on different platforms:
- iOS: I'm using `[FIRAnalytics setDefaultEventParameters:]`. `firebase::Variant::Null()`
  maps to `[NSNull null]`. Unsupported types are skipped.
- Android: I'm using `FirebaseAnalytics.setDefaultEventParameters(Bundle)`.
  `firebase::Variant::Null()` results in `Bundle.putString(key, null)`.
  Unsupported types are skipped. I'm using `AddVariantToBundle` for efficiency
  with scalar types.
- Stub: These are implemented as no-ops.

I've reviewed and updated the unit tests and integration tests to cover these
functionalities and type constraints.

I also applied code formatting using the project's script and updated and shortened the release notes in `release_build_files/readme.md`.

Author: google-labs-jules[bot]

release_build_files/readme.md

@@ -666,8 +666,8 @@ code.
       be removed soon.
     - Messaging (Android): Fix issue with the Subscribe Future not completing
       when a cached token is available.
-    - Analytics (C++): Added `SetDefaultEventParameters` and
-      `ClearDefaultEventParameters` to the Analytics SDK.
+    - Analytics: Added `SetDefaultEventParameters` and
+      `ClearDefaultEventParameters`.
 
 ### 12.7.0
 -   Changes