Wrong receiver is generated for variable-as-function call on object.

Move 'generateExpressionForReferencedDescriptor' to CallGenerator,
use it in 'generateCall',
add PSI-free versions of some utility methods so that call elements can
be generated when we're already deep in ResolvedCall generation
and have forgotten about PSI.

compiler/testData/ir/irText/expressions/objectAsCallable.kt

@@ -0,0 +1,9 @@
+object A
+
+enum class En { X }
+
+operator fun A.invoke(i: Int) = i
+operator fun En.invoke(i: Int) = i
+
+val test1 = A(42)
+val test2 = En.X(42)