Migrate Automatic Exec Groups by adding a toolchain parameter to the affected actions

[kotlaja]

This is a step forward for the full migration of Automatic Exec Groups (AEGs). This change will be effective once AEGs are enabled.

Goal of this migration:

• Each toolchain type should have its own execution platform. Before this change, the execution platform was selected on a rule base, not on a toolchain type base.
• Each action which uses a tool coming from a toolchain should specify the toolchain type inside ctx.action.{run, run_shell} toolchain attribute.

The affected action uses tools from cpp toolchain. Hence, cpp toolchain is added to the toolchain param.

[fruffy]

@smolkaj @kheradmandG

[smolkaj]

Thanks for approving, LGTM.