[develop2] refactor around cli and api

[memsharded]

Pure refactors, no functional change:

• Renamed ConanAPIV2 -> ConanAPI (it is confusing for the users to mix 2.0 version with api version, this is the first public documented api)
• Moved _get_conanfile_path() helper, used in many places to its own LocalAPI api. It seems there are other bits of code that we will have to find a location for them, and LocalAPI could be good. We could discuss if editable api could be part of this, maybe yes
• Moved deployers code from api to its own internal deploy.py module
• Moved some helpers related to CLI arguments to args.py

TODO: (in another PR). Find a place to the global graph_compute() function, used in multiple commands.