Suggested: Apply Singleton pattern to EuRxManager

[designe]

Discussed in https://github.com/orgs/euphony-io/discussions/254

^{Originally posted by phj0407 September 13, 2022}

AS-IS

While I apply Euphony library for sample app project, I find using one more object can cause malfunciton. I think applying singleton pattern to EuRxManager can prevent potential issue.

TO-DO

Now, EuRxManager have 3 constructor.

public EuRxManager() {
		mOption = EuOption.builder()
				.modeWith(EuOption.ModeType.DEFAULT)
				.encodingWith(EuOption.CodingType.BASE16)
				.modulationWith(EuOption.ModulationType.FSK)
				.build();
	}

	public EuRxManager(RxEngineType engineType) {
		rxEngineType = engineType;
		if(rxEngineType == RxEngineType.EUPHONY_NATIVE_ENGINE)
			nativeCore = EuNativeConnector.getInstance();
		else
			nativeCore = null;
	}

	public EuRxManager(EuOption.ModeType mode) {
		mOption = EuOption.builder()
				.modeWith(mode)
				.build();
	}

I think public EuRxManager(),public EuRxManager(EuOption.ModeType mode) can be combined. And initializing nativeCore can be solved seperately by add new method.