Flutter cloud_firestoreプラグインを入れると64kエラーになる時の解決策

cloud_firestoreを試そうとサンプルを実行していたところ、以下の問題にぶつかりました。

現象

cloud_firestoreプラグイン導入後、ビルドが通りませんでした。

環境

Flutter/Android
firebase_core: ^0.4.0
cloud_firestore: ^0.12.5+2

エラーメッセージ

D8: Cannot fit requested classes in a single dex file (# methods: 74144 > 65536)

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':app:transformDexArchiveWithExternalLibsDexMergerForDebug'.
> com.android.builder.dexing.DexArchiveMergerException: Error while merging dex archives:

/省略/

  The number of method references in a .dex file cannot exceed 64K.
  Learn how to resolve this issue at https://developer.android.com/tools/building/multidex.html

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

BUILD FAILED in 3s
Finished with error: Gradle task assembleDebug failed with exit code 1