* feat(parser): adopt slang as the default SystemVerilog frontend
- replace export RTL parsing with slang elaboration
- replace pack transaction parsing with slang
- remove Verible from normal parser and packaging flows
- fetch pinned slang and fmt releases via make init
- refresh tests and docs for the slang-based workflow
* fix(codegen): resolve filelist-relative inputs and quiet false missing-file logs
* refact(codegen): tidy up content about `_with_slang`
* feat(verible): Remove content about verible
* fix(gcc): Fix ignored attributes in gcc
* fix(parser): avoid gcc ambiguous overload in uvm parse_sv_transactions
J. Wang