Add BlackOilFluidState::createFluidState static factory method

[Copilot]

createFluidState logic in opm-simulators required passing many TypeTag boolean flags explicitly. Moving it into BlackOilFluidState as a static factory eliminates that redundancy — the class template parameters already encode all feature flags.

Changes

• BlackOilFluidState.hpp: Added createFluidState<ValueType> static method declaration; added <string_view> and <vector> includes.
• BlackOilFluidState_impl.hpp (new): Out-of-class implementation included at the bottom of the header. Three-step algorithm:
  1. Compute dissolution/vaporization factors (Rs, Rv, Rsw, Rvw) and invB per phase
  2. Compute reservoir-volume saturations from surface compositions, with mutual-dissolution corrections (Rs/Rv for oil+gas, Rsw/Rvw for water+gas); normalizes by the sum of all active phases (fixing a latent bug in the reference implementation that excluded water from the denominator)
  3. Normalize saturations; compute densities and enthalpies
  • Uses Opm::getValue() in error messages so formatting is safe with AD Evaluation types
  • static_assert(fluidSystemIsStatic) guards against use with non-static fluid systems
• test_blackoilfluidstate.cpp: Compile-time static_assert verifying the return type and signature of createFluidState<Evaluation>.

Usage

// Caller selects the desired specialization — no TypeTag needed.
using FluidState = BlackOilFluidState<Evaluation, FluidSystem,
    /*storeTemperature=*/true, /*storeEnthalpy=*/false,
    /*enableDissolution=*/true, /*enableVapwat=*/false,
    /*enableBrine=*/true>;

auto fs = FluidState::createFluidState(
    fluidComposition, pressure, temperature, saltConc, pvtRegionIdx, wellName);

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