Do not assemble deployedObject when not requested

[cameel]

Currently the runtime subassembly is always created if present, even if the evm.deployedBytecode/--bin-runtime output is not requested. It happens even when this output is not available, e.g. in command-line Yul mode. While this is not the slowest part of the pipeline, it's still a fair chunk of unnecessary processing that may add up in big projects and could be completely avoided.

Details

We have two separate places where this happens:

• In CompilerStack::assembleYul() for Solidity compilation (note that despite the name, this handles the non-IR assembling as well; we should rename the function).
• In YulStack::assembleWithDeployed() for pure Yul compilation.

We should make the deployed LinkerObject and optional result and only generate it when requested.

Note that code generation, optimization and Yul->EVM transformation is already being reused, because creation and deployed assemblies are a part of the same object tree. It's just the final assembling step that is performed independently.