Cannot generate tests for `infix` method

[tyuldashev]

Description
No tests are created when user tries to generate test for infix function or for class with only infix methods.

To Reproduce

Steps to reproduce the behavior:

1. In UTBot settings set Generated test language to Kotlin other leave default
2. Generate tests for following code

class InfixFuncs {
    infix fun Int.times(str: String) = str.repeat(this)
    infix fun String.onto(other: String) = Pair(this, other)
    infix fun Int.mult(other: Int) = other * this
}

Expected behavior

Tests are supposed to be generated.

Actual behavior

Error "No methods for test generation found" shown.

Visual proofs (screenshots, logs, images)

Additional context

[volivan239]

The problem here is that it is rather tricky to test non-toplevel extension-functions (at least if generating tests in Kotlin; from Java's perspective these are just usual methods, so no problems for Java) -- see discussion for examples.

I think it would be exciting if we support tests for such methods, however, maybe it is better not to propose them as testable at all, need to be discussed.

[EgorkaKulikov]

Possibly infix and operator functions are supported normally when they are top level, but need to verified. Not sure, do we really need them as not top level.