Issue with UHLODBuilder::ComputeHLODHash

The HLOD content hash used to detect changes and trigger rebuilds effectively
ignores everything hashed before the source-component loop — including the
result of UHLODBuilderSettings::ComputeHLODHash. The final hash is a function
of the source components only.

Root cause: UHLODBuilder::ComputeHLODHash opens a FHLODHashScope with
EFlags::ResetHash, which calls FArchiveCrc32::Reset() (zeroing the running
CRC) but never restores the previous CRC. Everything accumulated before the
loop is thrown away.

• Create a WorldPartition level
• Add an HLOD layer using UHLODBuilderInstancing

• Build it
• Modify a setting on UHLODBuilderInstancingSettings which changes the result of ComputeHLODHash.
• Build the HLODs
• Observe that the actors do not detect they need to rebuild.