perf(@angular-devkit/build-angular): minor sourcemap ignorelist improvements for esbuild builder

This provides a minor performance benefit for the generation of the Chrome sourcemap ignorelist
generation. Memory is shared were possible and string searching is reduced in certain cases.

(cherry picked from commit ac95732)

Author: clydin

packages/angular_devkit/build_angular/src/builders/browser-esbuild/sourcemap-ignorelist-plugin.ts

@@ -15,6 +15,12 @@ import type { Plugin } from 'esbuild';
  */
 const IGNORE_LIST_ID = 'x_google_ignoreList';
 
+/**
+ * The UTF-8 bytes for the node modules check text used to avoid unnecessary parsing
+ * of a full source map if not present in the source map data.
+ */
+const NODE_MODULE_BYTES = Buffer.from('node_modules/', 'utf-8');
+
 /**
  * Minimal sourcemap object required to create the ignore list.
  */
@@ -50,10 +56,15 @@ export function createSourcemapIngorelistPlugin(): Plugin {
             continue;
           }
 
-          const contents = Buffer.from(file.contents);
+          // Create a Buffer object that shares the memory of the output file contents
+          const contents = Buffer.from(
+            file.contents.buffer,
+            file.contents.byteOffset,
+            file.contents.byteLength,
+          );
 
           // Avoid parsing sourcemaps that have no node modules references
-          if (!contents.includes('node_modules/')) {
+          if (!contents.includes(NODE_MODULE_BYTES)) {
             continue;
           }
 
@@ -62,10 +73,8 @@ export function createSourcemapIngorelistPlugin(): Plugin {
 
           // Check and store the index of each source originating from a node modules directory
           for (let index = 0; index < map.sources.length; ++index) {
-            if (
-              map.sources[index].startsWith('node_modules/') ||
-              map.sources[index].includes('/node_modules/')
-            ) {
+            const location = map.sources[index].indexOf('node_modules/');
+            if (location === 0 || (location > 0 && map.sources[index][location - 1] === '/')) {
               ignoreList.push(index);
             }
           }