[IMM32] ImmGenerateMessage and ImmTranslateMessage (reactos#3914)

- Rewrite `ImmGenerateMessage` and `ImmTranslateMessage` functions.
- Rename `INPUTCONTEXTDX.bHasVKey` as `bNeedsTrans`.
- Move `TRANSMSG` structure into `ntuser.h`.
- Add `TRANSMSGLIST` structure into `ntuser.h`.
- Add `UNDETERMINESTRUCT` structure to `ddk/imm.h`.
- Modify `NtUserGetAppImeLevel` prototype.
CORE-11700

Author: katahiromz