[core] Simplify rows cache management

[flaviendelangle]

While working on #4927, I noticed that our cache structure had some complex legacy structure that was not useful anymore.

• Rename convertRowsPropToState into createRowsInternalCache
• Don't have branch behavior in createRowsInternalCache that was basically "do nothing", only call it when we do want to regenerate the cache
• Move all the utils in gridRowUtils
• Make apiRef.current.unstable_caches.rows non nullable, like for the state we can rely on the fact that the stat init is being done before the rest
• Flatten GridRowsInternalCache instead of having a value key storing almost everything
• Clean the naming, no variable related to the cache should be named state (otherwise we can have misunderstandings between what leaves in the state and in the cache)

[mui-bot]

These are the results for the performance tests:

Test case	Unit	Min	Max	Median	Mean	σ
Filter 100k rows	ms	286.5	618.9	529.3	460.08	135.4
Sort 100k rows	ms	667.4	1,140.4	667.4	928.16	167.89
Select 100k rows	ms	154.4	271.9	196.6	202.12	40.455
Deselect 100k rows	ms	113.2	209.4	178.8	168.34	38.766

Generated by 🚫 dangerJS against 5faa5bd

[alexfauquette]

Looks good to me but I never had to use the cache

[github-actions]

This pull request has conflicts, please resolve those before we can evaluate the pull request.

[m4theushw]

Much better with the values flattened.

[m4theushw]

What do you think of making explicit that they are props? Pick could also be used.

Suggested change

	getRowId: DataGridProcessedProps['getRowId'];
	loadingProp: DataGridProcessedProps['loading'];
	rows: GridRowsProp;
	getRowIdProp: DataGridProcessedProps['getRowId'];
	loadingProp: DataGridProcessedProps['loading'];
	rowsProp: DataGridProcessedProps['rows'];

[flaviendelangle]

Done