[VP] [PDVT-SH] Fix Coverity overrun-buffer-val in VEBOX common helpers

Add explicit static_cast<uint32_t>() to all dwSharedMocsOffset
assignments that compute negative signed offsets (e.g. 1 - 12 = -11).
These values are intentionally negative signed offsets from the current
DW to DW1 for MOCS bit patching. Without the cast, the implicit
int-to-uint32_t conversion triggers Coverity overrun-buffer-val warnings
because the unsigned wraparound produces values near UINT32_MAX.
Also add mhw_vebox_common_impl.h to media_srcs.cmake header list.