Convert ReactDOMComponent-test to createRoot

[kassens]

Convert ReactDOMComponent-test to createRoot

[rickhanlonii]

lgtm, there are a few tests that are flushing but not asserting between (i left some comments calling a couple out but there are more). Should we add assertions?

My thought process is:

• If we don't care about them flushing separately, then we can combine them inside the same act call.
• If we do care about flushing separately, then we should assert on their output to confirm they flush a different value

I don't care strongly, but it smelled funny so I thought I would mention it.

[rickhanlonii]

Should there be an assert in between?

[rickhanlonii]

Should we add asserts in between?

[kassens]

I added some in the places you highlighted, but otherwise, I want to focus on translating the tests w/o reworking them too much since there's a lot to go through.
The different acts should probably be there even without asserts as something like rendering <div> then <div style={...}> then finally <div> again would just be collapsed into no actual dom writes when batched.