fix(symlink/target): add `run` property on `ToolchainInfo` provider

BREAKING CHANGE: the `files_to_run` property has been removed from the `ToolchainInfo` provider. Use `info.default.files_to_run` instead.

A new `info.run` has been added that is `info.default.files_to_run` or `info.default.executable`.
This is a convenience property that can be passed to `ctx.actions.run#execute`.