[core] Flatten imports to speed up webpack build & node resolution

[oliviertassinari]

Summary 💡

Same as mui/material-ui#35840 but for MUI X.

We also miss an eslint rule to fail the build, but this is likely missing from the main eslint configuration, so a bit outside of the scope of X.

Examples 🌈

We should be able to import deep in:

mui-x/packages/grid/x-data-grid/src/hooks/features/sorting/useGridSorting.ts

Line 2 in 8757e19

import { unstable_useEnhancedEffect as useEnhancedEffect } from '@mui/utils';

mui-x/packages/x-date-pickers/src/DateTimePicker/dateTimePickerTabsClasses.ts

Line 4 in 8757e19

} from '@mui/utils';

mui-x/packages/x-charts/src/ChartsAxis/axisClasses.ts

Line 4 in 8757e19

} from '@mui/utils';

Motivation 🔦

It was raised in #10215.

Note that https://www.notion.so/mui-org/mui-utils-purpose-9a9fc9da3a004864b6c4e1f4d1f24f95 is a different problem/discussion. But regardless of either we import from base or utils, barrel imports shouldn't happen.

cc @romgrk maybe the type of performance topics you enjoy 😁. It's not about runtime performance though, mostly in dev mode.

[romgrk]

Just to be sure, by "importing deep" you mean:

-import { xxx } from '@mui/utils';
+import xxx from '@mui/utils/xxx';

right?

[oliviertassinari]

@romgrk Correct