Expose yosys extract -map similarly to SYNTH_EXTRA_MAPPING_FILE

[widlarizer]

Description

Yosys has functionality for subcircuit matching and replacing with modules, which can be instances of standard cells. An example of such a map file is in Yosys at techlibs/coolrunner2/tff_extract.v. For example, SKY130B doesn't have any extraction map files for turning muxes followed by flip flops to scan flops, which have been manually instantiated by some TinyTapeout 2 contributors to optimize area

Proposal

Allow users and PDKs to provide extra extraction map files like already implemented for the techmap command with SYNTH_EXTRA_MAPPING_FILE