[dart2wasm] Fix --extra-compiler-option parsing

Don't split the `--extra-compiler-option` values by commas, to allow
passing `-D`/`--define` flags like `-DFOO=a, b` as one argument.

Fixes the dart2wasm failure in #60346.

Change-Id: I9c621f93d4bcd4e35926e495735c8d15a3bac212
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/416581
Reviewed-by: Martin Kustermann <[email protected]>
Commit-Queue: Ömer Ağacan <[email protected]>

Author: osa1

pkg/dartdev/lib/src/commands/compile.dart

@@ -764,6 +764,7 @@ class CompileWasmCommand extends CompileSubcommandCommand {
         abbr: 'E',
         help: 'An extra option to pass to the dart2wasm compiler.',
         hide: !verbose,
+        splitCommas: false,
       )
       ..addOption(
         'optimization-level',