dillon1000/react

Update user timing to record when we are about to commit (#12384)

* Update user timing to record when we are about to commit

**what is the change?:**
After repeatedly logging '(React Tree Reconciliation)' we vary the
message slightly for the last reconciliation, which happens right before
we commit.

**why make this change?:**
When debugging performance in the devtools it will be helpful if we can
quickly see where the 'commit' happens in a potentially long list of
sliced '(React Tree Reconciliation)' logs.

**test plan:**
Built and ran one of the fixtures. Also ran the unit test.

(Flarnie will insert a screenshot)

* Ran prettier

* Fixes in response to code review

* Update snapshot tests

* Move isWorking assignment out of branches to top

* Stricter type for stopWorkLoopTimer args