While strictly speaking it depends on #157948, this could be started in parallel.

In #157948, we'll add dev_dependency: true|false to .flutter-plugins-dependencies.

This issue is tracking the Flutter Gradle plugin reading this new key/value pair, and on an explicit value of true, excluding a plugin from release branches. I say explicit value as we'll want a bit of backwards-compatibility, so in other words, I'd treat the following scenarios the following way:

{
  "name": "plugin-a",
  "path": "/path/to/plugin-a",
  "dependencies": ["plugin-b", "plugin-c"],
  "native_build": true
}

... should imply dev_dependency: false.

{
  "name": "plugin-a",
  "path": "/path/to/plugin-a",
  "dependencies": ["plugin-b", "plugin-c"],
  "native_build": true,
  "dev_dependency": false
}

... should specify dev_dependency: false.

{
  "name": "plugin-a",
  "path": "/path/to/plugin-a",
  "dependencies": ["plugin-b", "plugin-c"],
  "native_build": true,
  "dev_dependency": true
}

... should specify dev_dependency: true.