[Feature Request][package system] Better support for propagating options defined in Move.toml

[wrwg]

Right now, various places in the package system and CLI (e.g. running builds, tests, or the prover) have no way to access any options which might have been defined in the Move.toml, like language flavor, bytecode version, or other compiler or tool chain flags. This is because there is no design in place for sharing such global config info; rather there are a lot of static functions or struct methods on different data types. As an ugly workaround, we use environment variables like MOVE_BYTECODE_VERSION.

We should device a configuration model which gives uniform access to command line flags, configuration files, and Move.toml from everywhere. We may also want to leverage clap's capabilities to aggregate option structs to not have to redefine flags from independent tools for the package system.