[styled-engine] Add back removed internal function (#44421)

Author: mnajdova

packages/mui-styled-engine-sc/src/index.d.ts

@@ -81,6 +81,14 @@ export function internal_mutateStyles(
   processor: (styles: any) => any,
 ): void;
 
+// Not needed anymore, but fixes https://github.com/mui/material-ui/issues/44112
+// TODO: Remove it in v7
+// eslint-disable-next-line @typescript-eslint/naming-convention
+export function internal_processStyles(
+  tag: React.ElementType,
+  processor: (styles: any) => any,
+): void;
+
 // eslint-disable-next-line @typescript-eslint/naming-convention
 export function internal_serializeStyles<P>(styles: Interpolation<P>): object;
 

packages/mui-styled-engine-sc/src/index.js

@@ -48,6 +48,13 @@ export function internal_mutateStyles(tag, processor) {
   }
 }
 
+// Not needed anymore, but fixes https://github.com/mui/material-ui/issues/44112
+// TODO: Remove it in v7
+// eslint-disable-next-line @typescript-eslint/naming-convention
+export function internal_processStyles(tag, processor) {
+  return internal_mutateStyles(tag, processor);
+}
+
 // eslint-disable-next-line @typescript-eslint/naming-convention
 export function internal_serializeStyles(styles) {
   return styles;