Reland "Add a test for evicting unreachable modules from the global module cache (#74894)"

This reverts commit 35dacf2f.

And relands the original change with two additions so I can debug the failure on Arm/AArch64:
* Enable lldb step logging in the tests.
* Assert that the current plan is not the base plan at the spot I believe is calling PopPlan.

These will be removed and replaced with a proper fix once I see some failures on the bots,
I couldn't reproduce it locally.

(also, no sign of it on the x86_64 bot)