This patch introduces an intermediate Gradle build step to alter the behavior
of flutter_tools' Gradle project, specifically moving the creation of `build`
and `.gradle` directories from within the Nix Store to somewhere in `$HOME/.cache/flutter/nix-flutter-tools-gradle/$engineShortRev`.

Without this patch, flutter_tools' Gradle project tries to generate `build` and `.gradle`
directories within the Nix Store. Resulting in read-only errors when trying to build a
Flutter Android app at runtime.

This patch takes advantage of the fact settings.gradle takes priority over settings.gradle.kts to build the intermediate Gradle project
when a Flutter app runs `includeBuild("${settings.ext.flutterSdkPath}/packages/flutter_tools/gradle")`

`rootProject.buildFileName = "/dev/null"` so that the intermediate project doesn't use `build.gradle.kts` that's in the same directory.

The intermediate project makes a `settings.gradle` file in `$HOME/.cache/flutter/nix-flutter-tools-gradle/<short engine rev>/` and `includeBuild`s it.
This Gradle project will build the actual `packages/flutter_tools/gradle` project by setting
`rootProject.projectDir = new File("$settingsDir")` and `apply from: new File("$settingsDir/settings.gradle.kts")`.

Now the `.gradle` will be built in `$HOME/.cache/flutter/nix-flutter-tools-gradle/<short engine rev>/`, but `build` doesn't.
To move `build` to `$HOME/.cache/flutter/nix-flutter-tools-gradle/<short engine rev>/` as well, we need to set `buildDirectory`.
diff --git a/packages/flutter_tools/gradle/settings.gradle b/packages/flutter_tools/gradle/settings.gradle
new file mode 100644
index 0000000000..b2485c94b4
--- /dev/null
+++ b/packages/flutter_tools/gradle/settings.gradle
@@ -0,0 +1,19 @@
+rootProject.buildFileName = "/dev/null"
+
+def engineShortRev = (new File("$settingsDir/../../../bin/internal/engine.version")).text.take(10)
+def dir = new File("$System.env.HOME/.cache/flutter/nix-flutter-tools-gradle/$engineShortRev")
+dir.mkdirs()
+def file = new File(dir, "settings.gradle")
+
+file.text = """
+rootProject.projectDir = new File("$settingsDir")
+apply from: new File("$settingsDir/settings.gradle.kts")
+
+gradle.allprojects { project ->
+  project.beforeEvaluate {
+    project.layout.buildDirectory = new File("$dir/build")
+  }
+}
+"""
+
+includeBuild(dir)