[tool] Improve help info with build web --wasm flags (#125907)

Also fixed some comments

packages/flutter_tools/lib/src/commands/build_web.dart

@@ -98,13 +98,16 @@ class BuildWebCommand extends BuildSubCommand {
     );
     argParser.addFlag(
       'omit-type-checks',
-      help: 'Omit type checks in Wasm output.',
+      help: 'Omit type checks in Wasm output.\n'
+          'Reduces code size and improves performance, but may affect runtime correctness. Use with care.',
       negatable: false,
       hide: !featureFlags.isFlutterWebWasmEnabled,
     );
     argParser.addFlag(
       'wasm-opt',
-      help: 'Run wasm-opt on the output wasm module.',
+      help:
+          'Optimize output wasm using the Binaryen (https://github.com/WebAssembly/binaryen) tool.\n'
+          'Increases the build time, but will yield a smaller, faster output.',
       negatable: false,
       hide: !featureFlags.isFlutterWebWasmEnabled,
     );

packages/flutter_tools/lib/src/web/compiler_config.dart

@@ -147,14 +147,16 @@ class WasmCompilerConfig extends WebCompilerConfig {
         runWasmOpt: defines[kRunWasmOpt] == 'true',
       );
 
-  /// Build environment for [omitTypeChecks];
+  /// Build environment for [omitTypeChecks].
   static const String kOmitTypeChecks = 'WasmOmitTypeChecks';
+
+  /// Build environment for [runWasmOpt].
   static const String kRunWasmOpt = 'RunWasmOpt';
 
   /// If `omit-type-checks` should be passed to `dart2wasm`.
   final bool omitTypeChecks;
 
-  // Run wasm-opt on the resulting module.
+  /// Run wasm-opt on the resulting module.
   final bool runWasmOpt;
 
   @override