Support test methods with Kotlin suspend modifier

[IRus]

Goals

Support running suspend test in JUnit Jupiter:

class Kit {
    @Test 
    suspend fun foo() {
        delay(1000) // suspend call
        assertEquals(1, 1)
    } 
}

Currently, such test can be written this way:

class Kit {
    @Test 
    fun foo() = runBlocking {
        delay(1000) // suspend call
        assertEquals(1, 1)
        assertThrows { /* ... */ } 
        Unit // test should return void, but `assertThrows` returns `Throwable`, so `foo` returns `Throwable` too 
    } 
}

Also, will be nice to provide CoroutineScope through params, or as receiver in extension:

class Kit {
    suspend fun foo(scope: CoroutinesScope) {  /* ... */  } // (1)
    suspend fun CoroutinesScope.foo() {  /* ... */  } // (2)
}

1 and 2 actually the same on bytecode level. suspend is optional.

And finally, support for runBlockingTest:

class Kit {
    suspend fun foo(scope: TestCoroutinesScope) {  /* ... */  }
    suspend fun TestCoroutinesScope.foo() {  /* ... */  } 
}

What can be done currently

ParameterResolver can be used to provide stubs for Continuation, CoroutineScope and TestCoroutineScope. These stub arguments can be replaced with real arguments in invocation.

Problems

Current extensions points not enough to implement this feature as extensions, since:

1. Discovery. Jupiter discovers tests that returns void, but suspend fun returns Object;
2. Invocation. InvocationInterceptor in 5.5-M1(SNAPSHOT) don't providing mechanism to override actual invocation, only to decoration of existing invocation. Conversion of method to kotlinFunction, and then executing using callSuspend is necessary to execute suspend fun.

Also, my slides about this topic.

[sormuras]

Related to #1851

[marcphilipp]

@IRus This is not resolved by #2042, is it?

[IRus]

@marcphilipp Yes, not resolved, this is different issues

[xeruf]

Please resolve this! My tests looked all fine until I discovered that they were not run at all anymore after adding suspending functions :/