[PH2][Settings][Refactor]

[PH2][Settings][Refactor]

Initial Design :
```
class Http2ClientTransport {
    private :

	PendingIncomingSettings object1;
	SettingsTimeoutManager object2;
	Http2SettingsManager object3;

    public :

	void TypicalTransportFunction(){
	    ... other non-settings work ...
		object1.DetailedWork1();
		object2.DetailedWork2();
		object3.DetailedWork3();
	    ... other non-settings work ...
	}
};
```

New Design

```
class Http2ClientTransport{
	SettingsPromiseManager settings_manager_;

	void TypicalTransportFunction(){
	    ... other non-settings work ...
		settings_manager_.SomeWork();
	    ... other non-settings work ...
	}
};

class SettingsPromiseManager{
	Http2SettingsManager settings_;

	void SomeWork(){
		DetailedWork1();
		DetailedWork2();
		settings_.DetailedWork3();
	}

	private :
		DetailedWork1();
		DetailedWork2();
}
```

Refactor Step 1
1. Merge class `SettingsTimeoutManager` and `PendingIncomingSettings` into a new class named `SettingsPromiseManager`
2. Replace usage of `PendingIncomingSettings` and `SettingsTimeoutManager` with usage of `SettingsPromiseManager`
3. Replace `pending_incoming_settings_` with `transport_settings_`

Future Steps
1. Step 2 : Move object of `Http2SettingsManager` class into `SettingsPromiseManager` and the `Http2ClientTransport` will use  `Http2SettingsManager` via `SettingsPromiseManager`
2. Step 3 : Earlier the `Http2ClientTransport` class had interactions between `Http2SettingsManager` `SettingsTimeoutManager` and `PendingIncomingSettings` in the transport. Move this into our new `SettingsPromiseManager` class. This will make the transport lean. This PR will need careful review to the business logic. This will also make multiple permutations of settings very easily testable and debuggable.
3. Step 4 : Rename variables and functions to ensure that the common confusion between SENT and RECEIVED settings is not there. The current structure and naming makes it hard to differentiate. We really have wasted a LOT of time here.
4. Step 5 : Write unit tests for `SettingsPromiseManager` class, modelling scenarios similar to how the transport will be using the settings. Also add missing tests to `Http2SettingsManager` if needed.

PiperOrigin-RevId: 837359318