MSGate not in top level

[dabacon]

Description of the issue

cirq.MSGate does not exist, but cirq.ops.MSGate does. Think it should be at the top level too?

[github-actions[bot]]

This issue is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 30 days

[dstrain115]

Adding triage discuss to determine whether to expose at the top level.

[angelo-laskaris]

Ill take this issue