Consider to check read JSON representation for completeness

[mikir]

Currently, reading of partial JSON representation is supported without any notice. This feature is useful for debugging purposes if one can change value of only one field if required.

However, this behavior can lead to obscure errors during zserio object manipulation after reading of unintentionally partial JSON representation (this could happen easily for huge schemas).

Therefore consider to extend the fromJsonStream/String/File methods to accept some configuration options. The first configuration option could be a flag which would force automatic check of read JSON representation for completeness. This automatic check must be disabled by default (no change of current behavior).