feat(xcelium): add support for Cocotb + VHDL #535

Cocotb with VHDL is not working with the xcelium sim flow. This requires to add:

• The -NEW_VHPI_PROPAGATE_DELAY argument to the xrun -R command in the run method of the sim flow
• Enable the cocotb VHPI support:

vhpi = self._run_tool("cocotb-config", ["--lib-name-path", "vhpi", "xcelium"], quiet=True)[1]
env["GPI_EXTRA"] = f"{vhpi}:cocotbvhpi_entry_point"

This is officially documented in the cocotb:

• Cocotb | How-to Guides | Extending Existing Build Flows | Xcelium