Lantern EIL+TBT should use internally consistent FCP/TTI estimates

**Summary**
Currently in the optimistic/pessimistic lantern estimates for EIL and TBT we use the timing data computed by the FCP/FMP/TTI metric simulations as cutoffs but this leads to internally inconsistent data when the graphs are slightly different in EIL/TBT (e.g. TBT's graph has a TTI of 3.2s but the timing from the pessimistic simulation was 3.1s so we ignore the last 100ms of blocking time)

We should explore using the nodes of FCP that exist in EIL/TBT graphs and using *those* times within our EIL/TBT simulation results computation.

Discovered as part of #11666