Move cog setup logic into shell_utils so it can be used when any of these commands are run:

- `m`
- `lunch`
- `source build/envsetup.sh`

this will set up the symlink properly regardless of the order of commands so users don't get stuck with a broken build

Bug: 362337892
Change-Id: Ibd3b262107dfc1024cd83ab8aeb33a299fb0ffb2