Copy 9.3.0 change notes from C++ 9.3.0 change notes

[AlmostMatt]

Description

Copies the change notes from c++ 9.3.0 release notes

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Testing

n/a

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Type of Change

Place an x the applicable box:

• Bug fix. Add the issue # below if applicable.
• New feature. A non-breaking change which adds functionality.
• [x ] Other, such as a build process or documentation change.

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[github-actions]

❌  Integration test FAILED

Requested by @firebase-workflow-trigger[bot] on commit b2a7e4c
Last updated: Fri Jul 22 14:50 PDT 2022
View integration test log & download artifacts

Failures	Configs
analytics	[TEST] [ERROR] [2019] [macos] [1/6 Platform(s): iOS] [1/3 Test Device(s): simulator_target]
crashlytics	[TEST] [FLAKINESS] [2019] [macos] [1/6 Platform(s): iOS] [1/3 Test Device(s): ios_target]
firestore	[BUILD] [ERROR] [2019] [macos] [1/3 Platform(s): Android]
functions	[TEST] [ERROR] [2019] [macos] [1/6 Platform(s): iOS] [1/3 Test Device(s): simulator_target]
installations	[TEST] [ERROR] [2019] [macos] [1/6 Platform(s): iOS] [1/3 Test Device(s): simulator_target]
messaging	[TEST] [ERROR] [2019] [macos] [1/6 Platform(s): iOS] [1/3 Test Device(s): ios_target] [TEST] [FAILURE] [2019] [macos] [1/6 Platform(s): iOS] [1/3 Test Device(s): simulator_target]
remote_config	[TEST] [ERROR] [2019] [macos] [1/6 Platform(s): iOS] [1/3 Test Device(s): simulator_target]
storage	[TEST] [FAILURE] [2019] [macos] [4/6 Platform(s): macos ubuntu iOS windows] [1/3 Test Device(s): simulator_target] [TEST] [FLAKINESS] [2019] [macos] [1/6 Platform(s): Android] [1/3 Test Device(s): android_target]