feat(@angular-devkit/build-angular): add initial experimental esbuild-based application browser builder

An experimental browser application builder (`browser-esbuild`) has been introduced that leverages esbuild as the bundler.
This new builder is compatible with options of the current browser application builder (`browser`) and can be enabled
for experimentation purposes by replacing the `builder` field of `@angular-devkit/build-angular:browser` from an existing
project to `@angular-devkit/build-angular:browser-esbuild`. The builder will generate an ESM-based application and
provides support for ES2015+ compatible output with ES2020 as the default.

This builder is considered experimental and is not recommended for production applications.

Currently not all `browser` builder options and capabilities are supported with this experimental builder.
Additional support for these options may be added in the future.
The following options and capabilities are not currently supported:
* Stylesheet Preprocessors (only CSS styles are supported)
* Angular JIT mode (only AOT is supported)
* Localization [`localize`]
* Watch and dev-server modes [`watch`, `poll`, etc.]
* File replacements [`fileReplacements`]
* License text extraction [`extractLicenses`]
* Bundle budgets [`budgets`]
* Global scripts [`scripts`]
* Build stats JSON output [`statsJson`]
* Deploy URL [`deployURL`]
* CommonJS module warnings (no warnings will be generated for CommonJS package usage)
* Web Workers
* Service workers [`serviceWorker`, `ngswConfigPath`]

Author: clydin

packages/angular_devkit/build_angular/builders.json

@@ -11,6 +11,11 @@
       "schema": "./src/builders/browser/schema.json",
       "description": "Build a browser application."
     },
+    "browser-esbuild": {
+      "implementation": "./src/builders/browser-esbuild",
+      "schema": "./src/builders/browser/schema.json",
+      "description": "Build a browser application."
+    },
     "dev-server": {
       "implementation": "./src/builders/dev-server",
       "schema": "./src/builders/dev-server/schema.json",

packages/angular_devkit/build_angular/src/babel/webpack-loader.ts

@@ -39,7 +39,7 @@ let linkerPluginCreator:
  */
 let i18nPluginCreators: I18nPluginCreators | undefined;
 
-async function requiresLinking(path: string, source: string): Promise<boolean> {
+export async function requiresLinking(path: string, source: string): Promise<boolean> {
   // @angular/core and @angular/compiler will cause false positives
   // Also, TypeScript files do not require linking
   if (/[\\/]@angular[\\/](?:compiler|core)|\.tsx?$/.test(path)) {