Refactor to make the struct data types more easiliy inheritable

[0xdcota]

To facilitate access of struct data type in L2 implementation, refactor the following to be in an separate file.

https://github.com/Mint-Gold-Dust/v2-contracts/blob/abcd566e0d8a725b567e1fd128169efc04661808/contracts/marketplace/MintGoldDustMarketplace.sol#L31-L134