Fix class generation when using Forge generated ABI files

[nkramer44]

The ABI files that Forge generates after running forge build contain a "bytecode" field similar to the behavior of Truffle/Hardhat. However, Truffle/Hardhat set "bytecode" to a JSON string value, whereas Forge sets "bytecode" to an object that looks like this:

"bytecode": {
    "object": "...",
    "sourceMap": "...",
    "linkReferences": {}
}

When generating sources from ABI files using web3j-maven-plugin, the plugin properly generates Contract Java wrappers, however the BINARY field of the contract is always an empty string "". This is a sneaky error because it does not fail compilation, but makes it impossible to deploy the contract via the .deploy method. Even worse, calls to .deploy do not throw an exception or fail in any way, but rather end up deploying an empty contract on chain.

This PR updates JavaClassGeneratorMojo.parseAbiFile to handle Forge generated ABI files when parsing to correctly set the BINARY field of generated classes to "bytecode"."object" if "bytecode" is a JSON object (ie when generated by Forge), or "bytecode" when "bytecode" is a JSON String.

I added a sample ERC20.json ABI file generated via Forge to the test resources, as well as the test abi-sources project. Please let me know if there are additional tests I should write.