[core] Fix package layout inconsistencies

[DiegoAndai]

Fix two types issues discovered in mui/mui-x#16771:

• The @mui/utils/types export couldn't be imported because it didn't follow the index.d.ts file pattern
  • Error reference
  • Fix: Move the types.ts file into the an index.ts file inside types folder (commit)
• Some system types exports were exporting a non-existent default types
  • Error reference
  • Fix: Add missing default exports

[mui-bot]

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[Janpot]

Fix: Move the types.ts file into the an index.ts file inside types folder

👌

Fix: Split affected index.ts files into index.js and index.d.ts and remove the default export from index.d.ts

I'm not sure I fully understand, src/borders.js has a default export. It just looks like the declaration file that types this js file is missing a type for that. Don't we just need to fix src/borders.d.ts?

index f6f3a6f9ba..e91d39b6ab 100644
--- a/packages/mui-system/src/borders/borders.d.ts
+++ b/packages/mui-system/src/borders/borders.d.ts
@@ -1,4 +1,4 @@
-import { PropsFor, SimpleStyleFunction, borders } from '../Box';
+import { PropsFor, SimpleStyleFunction, ComposedStyleFunction } from '../Box';
 
 export const border: SimpleStyleFunction<'border'>;
 export const borderTop: SimpleStyleFunction<'borderTop'>;
@@ -11,4 +11,27 @@ export const borderRightColor: SimpleStyleFunction<'borderRightColor'>;
 export const borderBottomColor: SimpleStyleFunction<'borderBottomColor'>;
 export const borderLeftColor: SimpleStyleFunction<'borderLeftColor'>;
 export const borderRadius: SimpleStyleFunction<'borderRadius'>;
+export const outline: SimpleStyleFunction<'outline'>;
+export const outlineColor: SimpleStyleFunction<'outlineColor'>;
+
+declare const borders: ComposedStyleFunction<
+  [
+    typeof border,
+    typeof borderTop,
+    typeof borderRight,
+    typeof borderBottom,
+    typeof borderLeft,
+    typeof borderColor,
+    typeof borderTopColor,
+    typeof borderRightColor,
+    typeof borderBottomColor,
+    typeof borderLeftColor,
+    typeof borderRadius,
+    typeof outline,
+    typeof outlineColor,
+  ]
+>;
+
 export type BordersProps = PropsFor<typeof borders>;
+
+export default borders;

It looks like it's missing multiple exports in the declaration file. (And why are we importing utility types from ../Box?)

We should probably just consider converting these to typescript instead of manually trying to keep declaration files in sync.

[Janpot]

This is the default export in the .js file.

[Janpot]

This is how it's exported in the .js file

[Janpot]

I updated the declaration files. We'll look into migrating to typescript separately.

[DiegoAndai]

I confirmed that the latest build in this PR fixes the issue 👌🏼

Thanks @Janpot!