[bugfix] Refactor default exports to named exports

Replaced all default exports with named exports to improve module consistency and tree-shaking capabilities. This change ensures uniform export style across the codebase and aids in better maintainability and IDE auto-completion.

Bug Report: mui#43685

packages/mui-system/src/borders/index.ts

@@ -1,2 +1 @@
-export { default } from './borders';
 export * from './borders';

packages/mui-system/src/cssGrid/index.ts

@@ -1,2 +1 @@
-export { default } from './cssGrid';
 export * from './cssGrid';

packages/mui-system/src/display/index.ts

@@ -1,2 +1 @@
-export { default } from './display';
 export * from './display';

packages/mui-system/src/flexbox/index.ts

@@ -1,2 +1 @@
-export { default } from './flexbox';
 export * from './flexbox';

packages/mui-system/src/palette/index.ts

@@ -1,2 +1 @@
-export { default } from './palette';
 export * from './palette';

packages/mui-system/src/positions/index.ts

@@ -1,2 +1 @@
-export { default } from './positions';
 export * from './positions';

packages/mui-system/src/shadows/index.ts

@@ -1 +1 @@
-export { default } from './shadows';
+export * from './shadows';

packages/mui-system/src/sizing/index.ts

@@ -1,2 +1 @@
-export { default } from './sizing';
 export * from './sizing';

packages/mui-system/src/spacing/index.ts

@@ -1,2 +1 @@
-export { default } from './spacing';
 export * from './spacing';

packages/mui-system/src/style/index.ts

@@ -1,2 +1 @@
-export { default } from './style';
 export * from './style';

packages/mui-system/src/typography/index.ts

@@ -1,2 +1 @@
-export { default } from './typography';
 export * from './typography';