[Solidity] Support for mapping keyword

[HOLLYwyh]

"mapping" is an important data structure in Solidity, and I sincerely hope that in the upcoming versions, ESBMC can support verification related to this data structure.

[lucasccordeiro]

Thanks for raising this issue, @HOLLYwyh.

@ChenfengWei0 is currently working on implementing this feature in ESBMC.

By the way, we're looking for relevant Solidity projects in the community. Please let us know if you want to recommend some open-source Solidity projects. We want to apply ESBMC to verify them formally.