MicroJson - JsonPropertyName class is missing the word Attribute at the end

[jeffjulian]

Describe the bug
When creating an attribute, it is standard (along with the other Json libraries) to call the class XYZAttribute. In the case of the JsonPropertyName class, this is not so. However, even one of the comments hints at it being named JsonPropertyNameAttribute.

My recommendation is to change the name to JsonPropertyNameAttribute as to be consistent with System.Text.Json and make porting to MicroJson an easier transition.