Bug fix of CoolProp fluid model

[PENGYAN777]

Proposed Changes

Two bugs related to CoolProp fluid model are found and solved:
1.Since there is no solver for two phase flow, then I ask CoolProp to assume the flow is single gas phase if the thermodynamics states are located on the liquid-vapor saturation curve.
2. CoolProp has some issues to update the thermodynamics states if the input pressure is very close critical pressure Pc, see here. So I let pressure equal to 0.99 Pc if pressure is very close to Pc.

Related Work

This work is related to PR #1806.

PR Checklist

• I am submitting my contribution to the develop branch.
• My contribution generates no new compiler warnings (try with --warnlevel=3 when using meson).
• My contribution is commented and consistent with SU2 style (https://su2code.github.io/docs_v7/Style-Guide/).
• I have added a test case that demonstrates my contribution, if necessary.
• I have updated appropriate documentation (Tutorials, Docs Page, config_template.cpp), if necessary.