Miscellaneous `Meta.partially_inline!` fixes (#56813)
This fixes up a couple of conspicuous problems I noticed when reviewing
I'm unsure we should have accepted this pass in Base to begin with... It
should at least be re-written to error on unexpected IR elements
(instead of performing an invalid transform silently), but the real
problem is that this pass is out-of-pipeline and so it doesn't run on
most user code and we have much worse coverage compared to passes in the
main Compiler.
(cherry picked from commit c1db3a419699a92c29ce2aff7547019eec3045a4)
