Improve echo cancellation settings ui

[Krzmbrzl]

This PR makes sure that the enablement of the echo cancellation ComboBox in the setting is done correctly (and on-the-fly: No need to press Apply for this to work) and if it is disabled, a tooltip will explain why.

Fixes #4110

Changelog

| Improved: Echo cancellation setting in the UI is now much more intuitive in regards to when and why it is disabled

[davidebeatrici]

Why not return the string directly instead of storing it in a variable?

[Krzmbrzl]

Why not return the string directly instead of storing it in a variable?

@davidebeatrici What code part are you talking about? 🤔

[davidebeatrici]

For example:

const QString ASIOConfig::name = QLatin1String("ASIOConfig");

const QString &ASIOConfig::getName() const {
	return ASIOConfig::name;
}

I would replace it with:

const QString &ASIOConfig::getName() const {
	return QLatin1String("ASIOConfig");
}

[Krzmbrzl]

Yeah you're right. I was thinking that I have to take special care here because I want to return a reference but as I'm using returning a const reference, I should be fine returning a string literal directly...

EDIT: Scratch that, it doesn't work. When I try to do that, I get

error: returning reference to temporary [-Werror=return-local-addr]

and if I try to make make the variable static inside the function body I get the same error.

Thus everything failed as I thought it would ☝️

[davidebeatrici]

Sorry, should've been:

const QString ASIOConfig::getName() const {
	return QLatin1String("ASIOConfig");
}

[Krzmbrzl]

Yeah that I didn't do because I don't see the need to copy the names all the time as they are in fact static. Thus I want to allocate them once and then use that instance ☝️

[davidebeatrici]

How many times is getName() called effectively?

[Krzmbrzl]

Probably not often enough for this to make a difference but I still wanted to do it "the best way". And I don't think it clutters the code in the way I did it 🤔

[davidebeatrici]

The memory usage is minimal anyway.