(🐞) Artificially literal bools not considered when performing reachability checks where branch terminates

There is already some disparity between naturally literal bools(annotated with Literal or narrowed) and artificially literal bools (platform, python-version, always-true, TYPE_CHECKING etc):

# mypy: always-true=foo
from typing import Literal

foo: bool

if not foo:
    print(1)  # no error ✅

bar: Literal[True]

if not bar:
    print(1)  # error: Statement is unreachable ✅

But this is not currently being applied to this situation:

# mypy: always-true=foo
from typing import Literal

foo: bool

def f1() -> None:
    if foo:
        return
    print(1)  # error: Statement is unreachable ❌

bar: Literal[True]

def f2() -> None:
    if bar:
        return
    print(1)  # error: Statement is unreachable ✅

Key:

✅ = correct behavior
❌ = sussy imposter behavior

Careful of #12325
Related: #11364

Start by reproducing the two reachability examples in the issue and compare the handling of artificially literal and naturally literal booleans. Read the context of #12325 and #11364 before changing behavior; done means the foo branch reports the same unreachable statement diagnostic as the bar branch without regressing the existing checks.