[Handoff][4/N] Fix Broken Parcelling of RemoteTask

A small issue in `RemoteTask`'s implementation of `Parcelable` was found in testing - `writeString8()` would sometimes cause `readString()` to under-read, due to `readString()` defaulting to `readString16()`.

Test: Validated manually. CTS tests in the future will fully test this
Bug: 400970610
Flag: android.companion.enable_task_continuity
Change-Id: I6f7bc4fca3b38c5626d4671775e30397c3516df5