rb_ivar_delete: also re-embed T_IMEMO/fields #116

Job	Run time
make (ruby, --enable-yjit --enable-zjit)	3m 20s
make (btest, --enable-zjit=dev)	2m 54s
make (zjit-check, --enable-yjit=dev --enable-zjit, 1.85.0)	3m 6s
make (zjit-test-all, --enable-zjit=dev, --seed=11831)	7m 23s
ZJIT macOS Arm64 result	3s
	16m 46s

Provide feedback