* SMZ3: Make GT fill behave like upstream SMZ3 multiworld GT fill
This means: All items local, 50% guaranteed filler, followed by possible
useful items, never progression.
* Fix item links
* SMZ3: Ensure in all cases, we remove the right item from the pool
Previously front fill would cause erratic errors on frozen, with the
cause immediately revealed by, on source, tripping the assert that was
added in #5109
* SMZ3: Truly, *properly* fix GT junk fill
After hours of diving deep into the upstream SMZ3 randomizer, it finally
behaves identically to how it does there
