- fixed external requirements set by StateTreeBrainComponent to find more specific actor classes first before defaulting on AActor
- added missing supported type FMassSharedFragment for MassStateTreeSchema
- moved StateTreeLinker to it own file and handle its potential failures
#rb mikko.mononen
#rnx
#preflight 624d98fd8e5ae00f0aca3123
[CL 19646871 by Yoan StAmant in ue5-main branch]