[core] Batch small changes

[oliviertassinari]

• [test] class names can't start with a digit a076c4b: Try document.querySelector('.109ja448cfod') it will throw.
  Discovered in https://github.com/mui-org/material-ui-x/blob/91b05ee8b6cc9fb1beab96187fd4308d4b7b294b/packages/grid/x-grid/src/XGrid.test.tsx#L71
• [docs] Sort subheaders ASC e41b125: I searching for the accordion, expecting it to be first in the list. but instead had the place of the previous Expension panel.
• [core] Convention suffix xIcon c2a03c0:
• [core] Use the same names for the commands 4f8ff2b: I was confused about the renaming happening between the root and docs workspaces.
• [Tooltip] Improve contrast cdc380e: [docs] Add links in the header #22210 (comment)
• [docs] Serial comma e9f428b: The serial comma (also called the Oxford comma) is the last comma before coordinating conjunction and the final item in a series. Its use is considered a matter of style and is cause for much debate. Many style guides require the serial comma, and a few advise against it. There are times when it must be used to avoid confusion or ambiguity. For the sake of consistency, we recommend always using the serial comma.
• [docs] standalone for consistency 5d8f90b: small typo
• [docs] Fix one missing property -> prop 5339484: small detail
• [docs] Expose createMuiTheme too 3a01c22: I wanted to test the behavior of the theme creator helper.
  It might be interesting to expose it to developers.
• [docs] Include notification in the description c09f43d: to help rank against "react notifications".
• [Stepper] Remove dead code fcd1545

[mui-pr-bot]

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