Refactor modularization code to avoid nested functions. NFC (#20962)

This also avoids the needs for an IIFE here, which makes the output code
much readable.

This also saves on code size.

Author: sbc100

test/code_size/hello_webgl2_wasm.json

@@ -1,10 +1,10 @@
 {
   "a.html": 569,
   "a.html.gz": 379,
-  "a.js": 4697,
+  "a.js": 4691,
   "a.js.gz": 2419,
   "a.wasm": 10482,
   "a.wasm.gz": 6728,
-  "total": 15748,
+  "total": 15742,
   "total_gz": 9526
 }

test/code_size/hello_webgl2_wasm2js.json

@@ -1,10 +1,10 @@
 {
   "a.html": 567,
   "a.html.gz": 379,
-  "a.js": 18022,
-  "a.js.gz": 8135,
+  "a.js": 18016,
+  "a.js.gz": 8139,
   "a.mem": 3123,
   "a.mem.gz": 2693,
-  "total": 21712,
-  "total_gz": 11207
+  "total": 21706,
+  "total_gz": 11211
 }

test/code_size/hello_webgl_wasm.json

@@ -1,10 +1,10 @@
 {
   "a.html": 569,
   "a.html.gz": 379,
-  "a.js": 4183,
+  "a.js": 4177,
   "a.js.gz": 2241,
   "a.wasm": 10482,
   "a.wasm.gz": 6728,
-  "total": 15234,
+  "total": 15228,
   "total_gz": 9348
 }

test/code_size/hello_webgl_wasm2js.json

@@ -1,10 +1,10 @@
 {
   "a.html": 567,
   "a.html.gz": 379,
-  "a.js": 17499,
-  "a.js.gz": 7958,
+  "a.js": 17493,
+  "a.js.gz": 7960,
   "a.mem": 3123,
   "a.mem.gz": 2693,
-  "total": 21189,
-  "total_gz": 11030
+  "total": 21183,
+  "total_gz": 11032
 }

tools/link.py

@@ -2325,23 +2325,15 @@ def modularize():
   if async_emit != '' and settings.EXPORT_NAME == 'config':
     diagnostics.warning('emcc', 'EXPORT_NAME should not be named "config" when targeting Safari')
 
-  src = '''
-%(maybe_async)sfunction(moduleArg = {}) {
-
-%(src)s
-
-  return %(return_value)s
-}
-''' % {
-    'maybe_async': async_emit,
-    'src': src,
-    'return_value': return_value,
-  }
-
   if settings.MINIMAL_RUNTIME and not settings.PTHREADS:
     # Single threaded MINIMAL_RUNTIME programs do not need access to
     # document.currentScript, so a simple export declaration is enough.
-    src = '/** @nocollapse */ var %s = %s' % (settings.EXPORT_NAME, src)
+    src = f'''\
+var {settings.EXPORT_NAME} = {async_emit}(moduleArg = {{}}) => {{
+  {src}
+  return {return_value};
+}};
+'''
   else:
     script_url_node = ''
     # When MODULARIZE this JS may be executed later,
@@ -2355,19 +2347,14 @@ def modularize():
       script_url = "typeof document !== 'undefined' && document.currentScript ? document.currentScript.src : undefined"
       if shared.target_environment_may_be('node'):
         script_url_node = "if (typeof __filename !== 'undefined') _scriptDir ||= __filename;"
-    src = '''%(node_imports)s
-var %(EXPORT_NAME)s = (() => {
-  var _scriptDir = %(script_url)s;
-  %(script_url_node)s
-  return (%(src)s);
-})();
-''' % {
-      'node_imports': node_es6_imports(),
-      'EXPORT_NAME': settings.EXPORT_NAME,
-      'script_url': script_url,
-      'script_url_node': script_url_node,
-      'src': src,
-    }
+    src = f'''{node_es6_imports()}
+var {settings.EXPORT_NAME} = {async_emit}(moduleArg = {{}}) => {{
+  var _scriptDir = {script_url};
+  {script_url_node}
+  {src}
+  return {return_value};
+}};
+'''
     # Given the async nature of how the Module function and Module object
     # come into existence in AudioWorkletGlobalScope, store the Module
     # function under a different variable name so that AudioWorkletGlobalScope
@@ -2378,14 +2365,14 @@ def modularize():
 
   # Export using a UMD style export, or ES6 exports if selected
   if settings.EXPORT_ES6:
-    src += 'export default %s;' % settings.EXPORT_NAME
+    src += f'export default {settings.EXPORT_NAME};'
   elif not settings.MINIMAL_RUNTIME:
-    src += '''\
+    src += f'''
 if (typeof exports === 'object' && typeof module === 'object')
-  module.exports = %(EXPORT_NAME)s;
+  module.exports = {settings.EXPORT_NAME};
 else if (typeof define === 'function' && define['amd'])
-  define([], () => %(EXPORT_NAME)s);
-''' % {'EXPORT_NAME': settings.EXPORT_NAME}
+  define([], () => {settings.EXPORT_NAME});
+'''
 
   final_js += '.modular.js'
   write_file(final_js, src)