Do not use a mixture of plugins{} and buildscript{}

Summary:
In our build logic we're mixing `plugins{}` and `buildscript{}`
which have unpredictable side-effect on the build classpath.

I'm moving over everything to use `plugins{}`. This is possible now
that we don't use build from source for New Architecture anymore.

Changelog:
[Internal] [Changed] - Do not use a mixture of plugins{} and buildscript{}

allow-large-files

Reviewed By: cipolleschi

Differential Revision: D43186768

fbshipit-source-id: dcd115bd9d7aadf5cb837b3a28598e274a092873

ReactAndroid/build.gradle

@@ -5,17 +5,12 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-buildscript {
-    dependencies {
-        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:${rootProject.hasProperty("kotlinVersion") ? rootProject.ext.kotlinVersion : KOTLIN_VERSION}"
-    }
-}
-
 plugins {
     id("com.android.library")
     id("com.facebook.react")
     id("de.undercouch.download")
     id("maven-publish")
+    id("org.jetbrains.kotlin.android")
 }
 
 import com.facebook.react.tasks.internal.*

ReactAndroid/gradle.properties

@@ -30,8 +30,5 @@ FOLLY_VERSION=2021.07.22.00
 GLOG_VERSION=0.3.5
 LIBEVENT_VERSION=2.1.12
 
-# Plugins Versions
-KOTLIN_VERSION=1.6.10
-
 android.useAndroidX=true
 android.enableJetifier=true

build.gradle.kts

@@ -35,6 +35,7 @@ buildscript {
   dependencies {
     classpath("com.android.tools.build:gradle:7.3.1")
     classpath("de.undercouch:gradle-download-task:5.0.1")
+    classpath("org.jetbrains.kotlin:kotlin-gradle-plugin:1.6.10")
   }
 }