Fix typechecking of promoted empty lists

The `'[]` case in `tc_infer_hs_type` is smart enough to handle arity-0 uses of
`'[]` (see the newly added `T23543` test case for an example), but the `'[]`
case in `tc_hs_type` was not. We fix this by changing the `tc_hs_type` case to
invoke `tc_infer_hs_type`, as prescribed in `Note [Future-proofing the type
checker]`.

There are some benign changes to test cases' expected output due to the new
code path using `forall a. [a]` as the kind of `'[]` rather than `[k]`.

Fixes #23543.