[CP-stable][tool] Fix libapp.so dropped from APK/app bundle - #188516

…188516)

### Issue Link:
What is the link to the issue this cherry-pick is addressing?

flutter#186810
flutter#187388
flutter#187553

### Impact Description:
What is the impact (ex. visual jank on Samsung phones, app crash, cannot ship an iOS app)?
Does it impact development (ex. flutter doctor crashes when Android Studio is installed),
or the shipping of production apps (the app crashes on launch).
This information is for domain experts and release engineers to understand the consequences of saying yes or no to the cherry pick.

The root cause either presents as the app crashing on startup, or the build failing with the message
> "Release app bundle failed to strip debug symbols from native libraries"

### Changelog Description:
Explain this cherry pick:
* In one line that is accessible to most Flutter developers.
* That describes the state prior to the fix.
* That includes which platforms are impacted.
See [best practices](https://github.com/flutter/flutter/blob/main/docs/releases/Hotfix-Documentation-Best-Practices.md) for examples.

< Replace with changelog description here >
[flutter/186810 flutter/187388 flutter/187553] When building android app bundles using flavors, or with an old app template combined with a plugin coming alphabetically before app, fixes problems with failing to include libapp.so in the produced app bundle.

### Workaround:
Is there a workaround for this issue?

For the case of the old app template combined with a plugin coming before "app" alphabetically, there is a workaround here flutter#186810 (comment). For the flavors case there is not a workaround.

### Risk:
What is the risk level of this cherry-pick?

### Test Coverage:
Are you confident that your fix is well-tested by automated tests?

### Validation Steps:
What are the steps to validate that this fix works?

1. make a fresh project
2. combine the subprojects in `android/build.gradle(.kts)`:
find 
```kotlin
subprojects {
    val newSubprojectBuildDir: Directory = newBuildDir.dir(project.name)
    project.layout.buildDirectory.value(newSubprojectBuildDir)
}

subprojects {
    project.evaluationDependsOn(":app")
}
```
and combine
```kotlin
subprojects {
    val newSubprojectBuildDir: Directory = newBuildDir.dir(project.name)
    project.layout.buildDirectory.value(newSubprojectBuildDir)
    project.evaluationDependsOn(":app")
}
```

3. add a plugin which comes alphabetically before "app"
4. also you will need to disable r8, due to how the templates have drifted over time.
```
// after signingConfig = signingConfigs.getByName("debug")

isMinifyEnabled = false
isShrinkResources = false
```

Also, you can separately test the repro steps listed in 
flutter#187388
to validate that this fixes the flavors-symptom of this underlying root cause.