KTOR-7698 Make ServiceLoader.load call optimizable by R8

[osipxd]

Subsystem
Client/Server

Motivation
KTOR-7698 ServiceLoader.load call is slow on Android

Solution
Upstreamed @whyoleg's optimization done by him in #4441 and applied it to all ServiceLoader.load calls.

[whyoleg]

note: it's better to recheck, that R8 will optimize this pattern with inline and reified usage. While from the code perspective it should be the same, I'm not confident, that the byte code will be the same.

[osipxd]

Yes, I'm not sure either 😅 I'm going to test it

[osipxd]

Yes, the optimization works!

During the testing I've found a more serious startup performance issue not related to ServiceLoader. We call typeOf during initialization of each plugin, and it is extremely slow when user have kotlin-reflect in dependencies.
Unoptimized service loader call takes ~20ms while initialization of HttpClient with five plugins installed takes more than a second! 😱 I'll file a new issue for this problem.

[osipxd]

KTOR-7715 Plugins’ initialization is slow on Android if kotlin-reflect is present

[osipxd]

I've tried to replace it with the following code, to retrieve iterator only once:

public inline fun <reified T> loadService(): Iterable<T>
    val iterator = ServiceLoader.load(
        T::class.java,
        T::class.java.classLoader,
    ).iterator()
    
    return Iterable { iterator }
}

But for some reason this change breaks serialization tests 🤔

[whyoleg]

iterators are single use, so they can not be used like this and looks like in serialization tests, result of loadService() is called multiple times and so when it's called second time, it will immediately start returning hasNext=false. (e.g https://pl.kotl.in/JkZSEveSX)

So looks like it's better to use Iterable { ... }.toList() as it was before