[material-ui][StepContent] Add slots and slotProps

[sai6855]

Part of #41281

This PR just adds slots and slotProps and doesn't deprecate TransitionComponent yet. See this discussion for why it's not deprecated yet #42167 (comment)

Once above discussion is resolved, I'd like to deprecate TransitionComponent in seperate PR

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

[mui-bot]

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[DiegoAndai]

@sai6855 I replied in #42157 (comment), but that's a special case. For TransitionComponent, lets deprecate as we did with the others: https://mui.com/material-ui/migration/migrating-from-deprecated-apis/#transitioncomponent

Besides that, the PR is good 👍🏼 but please let's deprecate in the same PR.

[sai6855]

For TransitionComponent, lets deprecate as we did with the others: https://mui.com/material-ui/migration/migrating-from-deprecated-apis/#transitioncomponent

In cases you shown above, TransitionComponent was used as <TransitionComponent/> where as in StepContent TransitionComponent is used as as={TransitionComponent}, because TransitionComponent is being used in as prop, i wanted to double check with you before deprecating.

• Backdrop depreaction https://github.com/mui/material-ui/pull/40677/files#diff-4c431bdfb8eaeba40fe63eaef8a47b5b6fe97d6f6ef7555feabfd763eef18e36L73
• Accordion depreaction https://github.com/mui/material-ui/pull/40418/files#diff-bbc688afec7bc090b1ad7bfd26cc2bedf991eca6fa3d2941b3dcbe04b3ee70a6L177

[DiegoAndai]

@sai6855 thanks for checking. I still think we should go forward with the deprecation, as:

• We should try to make all transition override APIs equivalent.
• I would expect this as -> slots.transition change not to be problematic as the others, because StepContentTransition has no styles in its styled call. So no styles would be lost when using slots.transition.

Again, thanks for checking first. I think it won't be a problem, but if users have issues, we can remove/change the deprecation in the future.