fix(ngcc): do not add trailing commas in UMD imports (#34545)

Previously, if `UmdRenderingFormatter#addImports()` was called with an
empty list of imports to add (i.e. no new imports were needed), it would
add trailing commas in several locations (arrays, function arguments,
function parameters), thus making the code imcompatible with legacy
browsers such as IE11.

This commit fixes it by ensuring that no trailing commas are added if
`addImports()` is called with an empty list of imports.
This is a follow-up to #34353.

Fixes #34525

PR Close #34545

packages/compiler-cli/ngcc/src/rendering/commonjs_rendering_formatter.ts

@@ -30,6 +30,11 @@ export class CommonJsRenderingFormatter extends Esm5RenderingFormatter {
    *  Add the imports below any in situ imports as `require` calls.
    */
   addImports(output: MagicString, imports: Import[], file: ts.SourceFile): void {
+    // Avoid unnecessary work if there are no imports to add.
+    if (imports.length === 0) {
+      return;
+    }
+
     const insertionPoint = this.findEndOfImports(file);
     const renderedImports =
         imports.map(i => `var ${i.qualifier} = require('${i.specifier}');\n`).join('');