test(middleware/immer): add runtime tests for immer middleware (#3471)

* test(middleware/immer): add runtime tests for immer middleware

* test(middleware/immer): rename non-function-updater test to describe produce bypass

The previous name ("should merge state when given a non-function updater")
implied merge semantics, which is vanilla setState's behavior. What the test
actually exercises is immer.ts:79, where a non-function updater bypasses
`produce`. Renaming to "should not apply produce when updater is not a
function" per @sukvvon's review feedback.