Added tests for EditorConfig.
#review-20127432 @aditya.ravichandran, @lauren.barnes
#preflight 628764ef2c34da686ac74123
#rnx
[CL 20292425 by sebastian nordgren in ue5-main branch]
Previously, I had assumed that FProperty::InitializeValue() would initialize a simple member (eg. a float) to the correct value, but this appears not to be the case, rather values are zero-initialized and the CDO stores the correct default values. In the case of structs, InitializeStruct() does in fact initialize correctly.
However, this means that we can't use GetMutableDefault() to get an instance of the UObject, since then we're changing what we're diffing against and serialize no values. Changed the usages of this pattern to use singletons instead.
#jira UE-141150
#review-19900014 @lauren.barnes, @aditya.ravichandran
#preflight 6267fa44a021c91a50f26a65
[CL 19919719 by sebastian nordgren in ue5-main branch]
