Add documentation for what to do when bumping the minimum sdk version supported by flutter (#179795)

Fixes #170807 

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

---------

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

docs/platforms/android/Update-Android-MinSdk-Version.md

@@ -0,0 +1,58 @@
+# Removing support for an Android API level in Flutter (go/flutter-android-remove-api-level)
+
+## Objective
+
+Provides a list of areas to consider and examples of former work for how to update Flutter to no longer support an old version of the Android API.
+
+### Overview
+After Flutter has decided to bump the minimum supported Android SDK, ideally through a justification document like http://goto.google.com/rfc-flutter-android-m-deprecation, this document covers what to update and suggests an order.
+
+#### Google3
+Googlers should start by following the Google3 migration steps defined in go/flutter-android-g3-minsdk-version.
+Google apps can be migrated to a higher minimum API level before Flutter drops support.
+
+#### Bump templates used in `flutter create`
+Templates take the least justification or configuration to bump.
+Example PR: https://github.com/flutter/flutter/pull/170882
+
+#### Add auto migration for apps targeting deprecated APIs.
+
+Example PR: https://github.com/flutter/flutter/pull/170882 `android_project_migration_test.dart`
+
+#### Modify tooling to enforce a new minimum version.
+
+Example PR: https://github.com/flutter/flutter/pull/170882 see `DependencyVersionChecker.kt` and `gradle_utils.dart`
+
+#### Update the engine minSdk and tests
+[Upgrading-Engine's-Android-API-version.md](Upgrading-Engine's-Android-API-version.md)
+
+#### Breaking change notice
+Create a breaking change notice for the next stable release.
+
+See "Minimum Android SDK has changed" in [Flutter 3.35 Technical Blog Post](https://blog.flutter.dev/whats-new-in-flutter-3-35-c58ef72e3766).
+
+#### Update documentation
+
+Update documentation page to indicate the old API is not tested: https://docs.flutter.dev/reference/supported-platforms.
+
+Example PR: https://github.com/flutter/website/pull/12230
+
+##### Issue hygiene
+Close all GitHub issues against the deprecated platform.
+
+#### Packages
+After a stable build is published with the new minimum Android API level.
+
+1. Update all existing Flutter maintained plugins to use the new stable Flutter version.
+2. Audit native Android code in any plugins that have no longer used codepaths and delete those codepaths.
+
+Example PRs:
+* https://github.com/flutter/packages/pull/9851
+* https://github.com/flutter/packages/pull/9987
+* https://github.com/flutter/packages/pull/10470
+
+
+#### Related documents
+
+Example tracking bug for `minSdk` 24 https://github.com/flutter/flutter/issues/170807
+Google3 documentation go/flutter-android-g3-minsdk-version