Add support for MUI v6

[djhi]

Problem

MUI v6 is out.

Solution

• Add support for MUI v6. Follow Add support for React 19 #10437
• react-admin packages will still use v5 in their devDependencies to ensure we don't use v6 only features inadvertently.
• The tutorial and e-commerce demo will use v6 so that we have an easy way to test v6

How To Test

Works with MUIv5

• build the RA packages locally from this branch
• create a new react-admin app: npm init react-admin react-admin-v6
• add the MUI deps: npm add @mui/material@^5.16.12 @mui/icons-material@^5.16.12
• copy the built packages to the react-admin-v6/node_modules directory
• Run the app & check your lock file

Works with MUIv6

• change the previous app MUI dependencies to ^6.0.0
• npm install
• Run the app & check your lock file

Additional Checks

• The PR targets master for a bugfix, or next for a feature

[djhi]

See https://mui.com/material-ui/migration/upgrade-to-v6/#box

[slax57]

Any changes in the CRM should be backported to https://github.com/marmelab/atomic-crm.

Besides, why do you need those changes? To my understanding, the MUI version used by the CRM demo shouldn't have changed, right?

UPDATE: I take it you kept those changes to prepare the compatibility with MUI v6, so I'm OK to keep them. But still, you'll need to open a PR to backport them to marmelab/atomic-crm.

[djhi]

Those changes work in v5 too. We were using deprecated features that have been removed in v6. I'd rather address them now than forget them