Apply kotlinx-atomicfu compiler plugin

[mvicsokolova]

Motivation
kotlinx-atomicfu is on the way to stabilization, as the next step I'm going to enable compiler transformations by default with the following getting rid of legacy transformations. For that it would be great to enable compiler plugin transformations in ktor. This PR enables JVM and Kotlin Native IR transformations performed by atomicfu-compiler-plugin.

I've disabled JS IR transformations, for now there is a discussion regarding removal of the JS part of the compiler plugin.

Solution
Minor changes were made in the code:

• replaced minusAssign/plusAssign operators with addAndGet call, because the operators are not supported by the compiler plugin.
• introduced atomic extension function to avoid passing atomic reference as a parameter (AtomicRef<*>.setContinuation(..)).
• atomic properties are recommended to be private, their values may be exposed via delegated properties.

[mvicsokolova]

@e5l Could you please take a look? 🙏🏻

Seems, the in the main branch the same tests are failing.