Add WriteTo API on JsonDocument and JsonProperty (dotnet/corefx#39367)
* Remove WriteProperty methods and rename WriteValue to WriteTo in JsonElement (dotnet/corefx#39037)
* Add WriteTo method in JsonDocument and JsonProperty (dotnet/corefx#39037)
* Remove all repeated tests from JsonDocument and JsonProperty for now.
* Added null check for Utf8JsonWriter parameter in WriteTo methods on JsonElement, JsonDocument and JsonProperty
* Code review changes
Commit migrated from https://github.com/dotnet/corefx/commit/
798468fb39d869a96104306483ed6ef4d63738ca