Now switch_id is no longer a metric to fail GSB mirrorable functions but circuit model is.

[tangxifan]

Motivate of the pull request

• To address an existing issue. If so, please provide a link to the issue:
• Breaking new feature. If so, please describe details in the description part.

Describe the technical details

What is currently done? (Provide issue link if applicable)

What does this pull request change?

This PR improves in the following aspects:

• Move the APIs to identify if GSBs are same in structures out of RRGSB class, to separated header/source files, as utility functions.
• Move the edge sorting APIs from GSB to utility functions.
• Now circuit model is used to judge if two nodes in a CB/SB are same in structure or not.
• Remove an unnecessary checks when comparing SB structures

Which part of the code base require a change

• VPR
• Tileable routing architecture generator
• OpenFPGA libraries
• FPGA-Verilog
• FPGA-Bitstream
• FPGA-SDC
• FPGA-SPICE
• Flow scripts
• Architecture library
• Cell library
• Documentation
• Regression tests
• Continous Integration (CI) scripts

Impact of the pull request

• Require a change on Quality of Results (QoR)
• Break back-compatibility. If so, please list who may be influenced.