* provided, an empty map is returned defensively so that [toTypeArgumentsMapping] doesn't conjure any error types. If you want to map
     * too few type arguments meaningfully, please provide filler types explicitly.
     */
    private fun toTypeArgumentsMapping(
        typeArguments: List<FirTypeProjection>,
        partiallyAppliedSymbol: KaPartiallyAppliedSymbol<*, *>,