[joy-ui][IconButton] Support loading prop

[Smileek]

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

This closes #36692

Mostly stolen from the Button component, but seemed to be a good task to start getting to know the project.

[mui-bot]

Netlify deploy preview

https://deploy-preview-40949--material-ui.netlify.app/

@mui/joy: parsed: +0.17% , gzip: +0.20%

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Generated by 🚫 dangerJS against 5cc23ad

[Smileek]

In the meantime, fixed a bug in the Button component:

ButtonGroup's disabled prop wasn't overridden, because the first part of (inProps.disabled || inProps.loading) ?? (buttonGroup.disabled || disabledProp || loading); resulted in (false || undefined) which is undefined.

[ZeeshanTamboli]

@Smileek, thanks for the pull request.

In the meantime, fixed a bug in the Button component:

ButtonGroup's disabled prop wasn't overridden, because the first part of (inProps.disabled || inProps.loading) ?? (buttonGroup.disabled || disabledProp || loading); resulted in (false || undefined) which is undefined.

Could you address this in a separate PR and undo the changes related to this in the current PR?

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Before reviewing the code, could you explain your use case for needing this feature? Is it necessary for your application?

[Smileek]

@ZeeshanTamboli sure. Here's another one: #41000

[ZeeshanTamboli]

@ZeeshanTamboli sure. Here's another one: #41000

Thanks for that pull request. I have reviewed it.

[Smileek]

@ZeeshanTamboli thanks for the review, everything is fixed: a4703b5

pnpm docs:build && pnpm docs:export runs well locally, so I believe Netlify failed for their own reason.

[ZeeshanTamboli]

@Smileek Thanks for your contribution!