Previously, when a candidate was found with an applicability that is
better than the current best applicability, all previous candidates were
thrown away. Now we keep them, unless the new applicability is
successful. If no successful candidates are found, we fully resolve all
the unsuccessful ones and select the ones with the least bad
applicability. This improves diagnostics for unresolved calls.
#KT-57844 Fixed
Previously the callee reference of a delegated constructor call is
always the same as the call itself. This violates the contract that no
two FIR elements can have identical sources. In addition, this sets the
entire call expression as the source of the callee expression.
This change instead sets the proper constructor ref as the callee.
Also fixed EXPLICIT_DELEGATION_CALL_REQUIRED type. It should be an error
instead of a warning.