Revert of Removes uint8_t from MachineRepresentation and MachineSemantic enums. (patchset #1 id:1 of https://codereview.chromium.org/2669113003/ )

Reason for revert:
Breaks bunch Wasm tests on Win64 (e.g., cctest/test-run-wasm/RunWasmCompiled_CallIndirect_EmptyTable).

Original issue's description:
> Removes uint8_t from MachineRepresentation and MachineSemantic enums.
>
> This works around a compiler bug that leads to incorrect masking of
> the semantic_ field in TruncatingUseInfoFromRepresentation.
>
> Patch from bulach@google.com
>
> BUG=
>
> Review-Url: https://codereview.chromium.org/2669113003
> Cr-Commit-Position: refs/heads/master@{#42925}
> Committed: https://chromium.googlesource.com/v8/v8/+/8c7fc377fd5c03e30cbf767cd22aba59178e0143

TBR=bulach@google.com,bmeurer@chromium.org,ulan@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=

Review-Url: https://codereview.chromium.org/2669213006
Cr-Commit-Position: refs/heads/master@{#42927}