store the composition fractions in SingleWellState

[GitPaean]

And use it in the fluid property calculation within the wellbore when calculating the connection pressure drop.

It only matters when the wells are SHUT-in and the surface_rates are all 0, under this situation, we can not calculate the fluid composition in the wellbore from the surface_rates.

Current implementation is an incomplete implementation. It is only done for StandardWell, producers and did not implement for the solvent cases. Solvent will be a phase and need a fraction also.

There might be other things need to be done also.

I put the PR here for information.