Add flag to decodeFromMap to allow implicit nulls

[mkotsbak]

What is your use-case and why do you need this feature?
Similar to explicitNulls for Json: https://kotlin.github.io/kotlinx.serialization/kotlinx-serialization-json/kotlinx-serialization-json/kotlinx.serialization.json/-json-configuration/index.html#kotlinx.serialization.json%2FJsonConfiguration%2FexplicitNulls%2F%23%2FPointingToDeclaration%2F

Describe the solution you'd like

inline fun <T> Properties.decodeFromMap(map: Map<String, Any>, explicitNulls: Boolean = true): T

where it is possible to set explicitNulls to false to allow missing values in map to be acceptable for nullable fields, they will be set to null.