Investigate `-prefix-serialized-debugging-options`

As of Swift 5.6(?) there is a new `-prefix-serialized-debugging-options` flag which is supposed to apply `-debug-prefix-map` flags to the serialized debugging options that we disable with the `swift.cacheable_swiftmodules` feature. Theoretically if we can switch to this flag, we can stop disabling these which might reduce the amount of work that has to be done in user's lldbinit files.