Remove IO_TYPE/BUFFER_TYPE min precision buffer workaround

The DXC compiler fix in PR microsoft#8274 handles min precision vector
load/store correctly at the DXIL level, so the test-side IO type
indirection (MIN_PRECISION, IO_TYPE, IO_OUT_TYPE, BUFFER_TYPE,
dispatchMinPrecisionTest, HLK_MIN_PRECISION_TEST) is no longer needed.
Min precision tests now use the same HLK_TEST/HLK_WAVEOP_TEST macros
and dispatch paths as all other types.

Co-authored-by: Copilot <[email protected]>

Author: alsepkow