Let's call builder lambdas (BL) a lambda that has non-fixed input type
projection at the moment of lambda arguments analysis, such lambdas
is a subject to be analyzed with builder inference
Due to bug in constraint system joining algorithm, currently system
of two or more such lambdas may lead to unsound type inference
Diagnostic added here should be reported in case when there are two
BL that shares a common constraint system, while not annotated with
@BuilderInference, as a protection against aforementioned bug
It's reported by ConstraintSystemCompleter when such situation has
occurred during builder inference phase, it is the same place that
decides wherever lambdas is subject to builder inference or not
KT-53740
Simon Ogorodnik