fix: stop an app's codegenConfig from hijacking this library's codegen (#201)

## Problem

When an app adds a TurboModule of its own and puts `codegenConfig` in
its root package.json, that config is applied to this library's codegen
instead of the library's own. `NativeCodePushSpec` is never generated,
the app's spec is written into the library's build directory, and
compilation fails:

```
node_modules/@bravemobile/react-native-code-push/android/app/src/main/java/
com/microsoft/codepush/react/CodePushNativeModule.java:44:
error: cannot find symbol
public class CodePushNativeModule extends NativeCodePushSpec {
```

The react-native gradle plugin's `findPackageJsonFile()` looks for
`../package.json` next to the gradle module first and falls back to the
app root when that file is missing. This library's module sat at
`android/app`, so the first lookup never resolved and the app root was
always read. It only stayed invisible while apps had no `codegenConfig`
of their own.

## Fix

The gradle module now lives at `android/`. The first lookup resolves to
the library's own package.json, which already carries the correct
`codegenConfig`. No second copy of the config is introduced, and this is
the layout most React Native libraries already use.

A separate commit removes the standalone gradle setup, which had stopped
working long ago: the wrapper pinned Gradle 2.4, the buildscript
classpath pinned AGP 1.3.0, `gradle.properties` was in a subproject
directory where Gradle never reads it, and Android unit tests run
through an example app. None of those files were reachable from any
build.

## Upgrading

An existing app holds an autolinking cache pointing at the old path, so
the first build after upgrading fails:

```
Configuring project ':bravemobile_react-native-code-push' without an existing directory is not allowed.
The configured projectDirectory '.../react-native-code-push/android/app' does not exist
```

Deleting these two directories clears it:

```
android/build/generated/autolinking
android/app/build/generated/autolinking
```

Nothing else changes for consumers. The gradle project name stays
`:bravemobile_react-native-code-push` because it is derived from the npm
package name, and the apply path for `codepush-export.gradle` is
untouched.

## Verification

codegen, Java compilation, unit tests and the CMake native build all
pass on the RN 0.77.3, 0.80.3, 0.83.2 and 0.86.0 example apps, covering
both ends of the supported range.

The reproduction case was checked on the lowest and highest versions:
with `codegenConfig` present in the app root, `NativeCodePushSpec.java`
is generated for the library and the app's own spec is generated for the
app module, each in its own place.

Author: floyd-soomgo

.gitignore

@@ -154,7 +154,7 @@ Ankh.NoLoad
 Examples/testapp_rn
 
 # Android debug build files (conflict ignoring #Visual Studio files)
-!android/app/src/debug/
+!android/src/debug/
 
 # prevent CLI code ignored (ignored by "[Rr]elease*/")
 !cli/commands/releaseCommand/

android/app/build.gradle

@@ -1,24 +1,58 @@
-// Top-level build file where you can add configuration options common to all sub-projects/modules.
+apply plugin: "com.android.library"
+apply plugin: "com.facebook.react"
 
-buildscript {
-    repositories {
-        google()
-        mavenCentral()
+def DEFAULT_COMPILE_SDK_VERSION = 26
+def DEFAULT_BUILD_TOOLS_VERSION = "26.0.3"
+def DEFAULT_TARGET_SDK_VERSION = 26
+def DEFAULT_MIN_SDK_VERSION = 16
+
+react {
+    jsRootDir = file("..")
+    libraryName = "RNCodePushSpec"
+    codegenJavaPackageName = "com.microsoft.codepush.react"
+}
+
+android {
+    namespace "com.microsoft.codepush.react"
+
+    compileSdkVersion rootProject.hasProperty('compileSdkVersion') ? rootProject.compileSdkVersion : DEFAULT_COMPILE_SDK_VERSION
+    buildToolsVersion rootProject.hasProperty('buildToolsVersion') ? rootProject.buildToolsVersion : DEFAULT_BUILD_TOOLS_VERSION
+
+    defaultConfig {
+        minSdkVersion rootProject.hasProperty('minSdkVersion') ? rootProject.minSdkVersion : DEFAULT_MIN_SDK_VERSION
+        targetSdkVersion rootProject.hasProperty('targetSdkVersion') ? rootProject.targetSdkVersion : DEFAULT_TARGET_SDK_VERSION
+        versionCode 1
+        versionName "1.0"
     }
-    dependencies {
-        classpath 'com.android.tools.build:gradle:1.3.0'
 
-        // NOTE: Do not place your application dependencies here; they belong
-        // in the individual module build.gradle files
+    lintOptions {
+        abortOnError false
     }
-}
 
-allprojects {
-    android {
-        namespace "com.microsoft.codepush.react"
+    defaultConfig {
+        consumerProguardFiles 'proguard-rules.pro'
     }
-    repositories {
-        mavenLocal()
-        mavenCentral()
+
+    // Builds the binary patch applier. Its sources are the shared ones at the root of the
+    // repository, which the CMake file points at; nothing is compiled twice.
+    externalNativeBuild {
+        cmake {
+            path "src/main/cpp/CMakeLists.txt"
+        }
+    }
+
+    testOptions {
+        // The unit tests exercise plain logic, so the android framework classes they touch
+        // in passing (logging above all) are allowed to do nothing instead of throwing.
+        unitTests.returnDefaultValues = true
     }
 }
+
+dependencies {
+    implementation "com.facebook.react:react-native:+"
+
+    testImplementation "junit:junit:4.13.2"
+    // org.json ships as stubs in the android framework jar, and the unit tests parse real
+    // manifests, so they need an implementation that actually parses.
+    testImplementation "org.json:json:20231013"
+}