add setting for Verilog external code library path

[renyangang]

when using external Verilog code components, it is necessary to introduce the Verilog code library that has already been written externally. If used multiple times, multiple reference paths need to be configured. This modification adds a global setting item, configuring an external Verilog code library search path. This way, as long as configured once, multiple references can be made without configuring this path in each component
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