This PR adds `@[expose]` to `Lean.Grind.abstractFn` and
`Lean.Grind.simpMatchDiscrsOnly` so that the kernel can unfold them when
type-checking `grind`-produced proofs inside `module` blocks. Other
similar gadgets (`nestedDecidable`, `PreMatchCond`, `alreadyNorm`) were
already exposed; these two were simply missed.
Closes https://github.com/leanprover/lean4/issues/13167