[MMSYS] Multimedia Control Panel diverse fixes (#4572)

[MMSYS] Multimedia Control Panel diverse fixes (#4572)

- Use Unicode (WCHAR) instead of TCHAR
- Code formatting
- Use string safe functions
- Close handles after calling `CreateProcess`
- Save sound path as `REG_EXPAND_SZ` only if the path
  contains '%' character, like Windows does
- Fix `wcsdup` leaks

Reviewed-by: Mark Jansen <mark.jansen@reactos.org>
Reviewed-by: Hermès Bélusca-Maïto <hermes.belusca-maito@reactos.org>
Reviewed-by: Katayama Hirofumi MZ <katayama.hirofumi.mz@gmail.com>
Reviewed-by: Stanislav Motylkov <x86corez@gmail.com>