refactor(@angular/build): add explicit type annotations to avoid inferred types

This refactor resolves an issue where the inferred type of `renderSassStylesheet` required an external reference, which could affect portability.

Fixes the following error:
```
packages/angular/build/src/tools/sass/worker.ts:59:31 - error TS2742: The inferred type of 'renderSassStylesheet' cannot be named without a reference to '../../../../../../external/npm/node_modules/source-map-js/source-map'. This is likely not portable. A type annotation is necessary.
```
Explicit type annotation added to `renderSassStylesheet` function to prevent reliance on inferred types.

**Note:** Ensure compatibility with Windows Bazel builds.

Author: alan-agius4

packages/angular/build/src/tools/sass/worker.ts

@@ -56,7 +56,29 @@ interface RenderRequestMessage {
   rebase: boolean;
 }
 
-export default async function renderSassStylesheet(request: RenderRequestMessage) {
+interface RenderResult {
+  warnings: SerializableWarningMessage[] | undefined;
+  result: {
+    css: string;
+    loadedUrls: string[];
+    sourceMap?: RawSourceMap;
+  };
+}
+
+interface RenderError {
+  warnings: SerializableWarningMessage[] | undefined;
+  error: {
+    message: string;
+    stack?: string;
+    span?: Omit<SourceSpan, 'url'> & { url?: string };
+    sassMessage?: string;
+    sassStack?: string;
+  };
+}
+
+export default async function renderSassStylesheet(
+  request: RenderRequestMessage,
+): Promise<RenderResult | RenderError> {
   const { importerChannel, hasLogger, source, options, rebase } = request;
 
   const entryDirectory = dirname(options.url);
@@ -164,6 +186,7 @@ export default async function renderSassStylesheet(request: RenderRequestMessage
       warnings,
       result: {
         ...result,
+        sourceMap: result.sourceMap as unknown as RawSourceMap | undefined,
         // URL is not serializable so to convert to string here and back to URL in the parent.
         loadedUrls: result.loadedUrls.map((p) => fileURLToPath(p)),
       },