fix(compiler): evaluate trailing empty switch cases

[yavon007]

A trailing empty switch case was discarded during AOT lowering. Its condition was never evaluated, and even a matching trailing case could incorrectly execute an earlier default branch.

Keep trailing case/default labels as an empty case group so the existing ordered comparison logic evaluates them and suppresses the default when they match. Add a PHPT covering both observable condition side effects and default suppression.

Validation on Linux ARM64 with PHP 8.5.10:

• New regression fails before the fix and passes afterward; its expected output matches plain PHP.
• tests/compiler/switch: 7/7 passed with native AOT compilation.
• Applied together with the separate switch-type-comparison fix: all three new PHPT regressions passed.
• git diff --check passed.