Implement Standard Platform Transitions

[katre]

This is a tracking issue for the implementation of Standard Platform Transitions.

The steps required are:

• [ ] Implement platform_data
• [ ] Implement change_platform (for a static platform)
• [ ] Implement change_platform (with a platform attribute)
• [ ] Implement other features as needed

The implementation can be based off of Aspect's platform_transition_binary and Skylib's native_binary.

Note that the platform_data implementation should:

• Make sure that the new files are executable
• Make a copy, not just a symlink
• Work with rules such as cc_binary, py_binary, and sh_binary.

[katre]

Ping @gregestren for any comments or corrections, and then let's figure out who can do the work.

[gregestren]

Makes sense.

Keeping all the above in mind, I'd start with a MVP that we have confidence serves Pigweed's needs. Publish it and let Pigweed integrate as soon as possible, so we can meet our quarterly expectations. :)

Then extend to the rest more casually.

@aiuto if there are any other specific cc_binary projects you're thinking of please share. Same goes for anyone else with specific requests (@fmeum , @keith, etc.)