[WIP] Switching from Synlig to Yosys-Slang

[loglav03]

Description

Replaced Synlig with the Yosys-Slang plugin for Yosys for reading SystemVerilog.

Related Issue

1. System Verilog support is broken due to compilation error in F4PGA plugin #2821
2. Embed slang-yosys plugin as a SystemVerilog frontend for yosys #3108

Motivation and Context

Synlig has a lot of overhead when building with the vtr build system leading to issues when building in CI and sometimes locally. Synlig is also poorly maintained. Yosys-Slang has significantly less overhead, can easily be implemented as a plugin for yosys, and is regularly maintained.

How Has This Been Tested?

Has been tested with the vtr_reg_system_verilog tests [PASSED]
Going to test with extra tests from the Yosys-Slang repo: https://github.com/povik/yosys-slang/tree/master/tests

Types of changes

• [ x] Bug fix (change which fixes an issue)
• New feature (change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [ x] My change requires a change to the documentation
• I have updated the documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed