Flutter Android build: Automate the upload of debug symbols

[orkun1675]

Use case

See https://github.com/orgs/codemagic-ci-cd/discussions/2900#discussioncomment-11818663.

TLDR: When Flutter apps use obfucation the debug symbols are not included in the .aab due to a long standing issue. This requires developers to manually generate and upload a zip file every time they want to release a build (or risk not getting readable logs/Crashylytics).

This is a very prevalent complaint:

• [Android] Document fix for warning "native debug symbols are missing in appbundle" when uploading app to playconsole flutter/flutter#98773 has 21 upvotes.
• https://stackoverflow.com/questions/62568757/playstore-error-app-bundle-contains-native-code-and-youve-not-uploaded-debug/79104473#79104473 has hundreds of engagements
• https://www.youtube.com/watch?v=3ieKwhmQg7I&t=405s&ab_channel=iRekhaTechSolutions has thousands of views

Idea

First a script can be used to generate the debug symbols zip:

- name: Create native debug symbols
  script: |
    SYMBOLS_DIR=$CM_BUILD_DIR/build/app/intermediates/stripped_native_libs/release/stripReleaseDebugSymbols/out/lib
    SYMBOLS_FILE=$CM_BUILD_DIR/build/android_native_debug_symbols.zip
    rm -rf $SYMBOLS_DIR/.crashlytics
    cd $SYMBOLS_DIR && zip -r $SYMBOLS_FILE . && cd -

Then we can utilize the Google Play Developer API upload endpoint to upload this zip to the Play store. Note that we will need to specify deobfuscationFileType=nativeCode when calling this endpoint.

[orkun1675]

Updated original post with the codemagic.yaml script we use that is verified working.