[material-ui][types] Make slots partial in `CreateSlotsAndSlotProp`type

[lhilgert9]

@DiegoAndai As already discussed in #41875, here is the PR to make the slots in the CreateSlotsAndSlotProps help type partial to avoid possible errors.

• [x] I have followed (at least) the PR section of the contributing guide.

[mui-bot]

Netlify deploy preview

https://deploy-preview-42077--material-ui.netlify.app/

Bundle size report

No bundle size changes (Toolpad) No bundle size changes

Generated by :no_entry_sign: dangerJS against 6165656dd6d4efbad489c5d7e3fbf0264941fd9c

[DiegoAndai]

Thanks for working on this @lhilgert9!

I'm on board with the changes. What do you think, @siriwatknp? Does this make sense to you?

[lhilgert9]

@DiegoAndai @siriwatknp What about this one?

[ZeeshanTamboli]

@DiegoAndai @siriwatknp Can you review this? The PR has been open for a while.

[DiegoAndai]

@lhilgert9 I'm so sorry for the late reply. The v6 stable release consumed most of my time in the past month.

I'm still on board with this change. What do you think about removing ? for the slots definitions which are now redundant, would you be up to do it in this same PR?

[lhilgert9]

@DiegoAndai Done🚀 Hope I got them all.