title: Gradle Kotlin DSL: Define Android build tools version in unique place
body: <p>I am using Android Studio 4.0 and I added <code>buildSrc</code> module in a multi-module project to manage dependency versions. Inside <code>buildSrc</code> i have <code>Dependencies</code> object and <code>Version</code> object to use  <code>kotlin-dsl</code> in the <code>build.gradle.kts</code>, The problem it's I can't access to Constants object from  <code>gradle.kts</code> and I have 2 versions of <code>com.android.tools.build:gradle:4.0.0</code> and I need this dependency for my custom plugins, How I can have only one version of the buildtools?</p>
  
  <pre><code>//Dependencies.kt
  object PluginDependencies {
   const val buildTools = "com.android.tools.build:gradle:${Versions.buildTools}"
  }
  
  //Versions.kt
  object Versions {
  const val buildTools = "4.0.0" 
  }
  </code></pre>
  
  <p>I have this in my <code>build.gradle.kts</code></p>
  
  <pre><code>plugins {
      `kotlin-dsl`
  }
  gradlePlugin {
      plugins {
          register("CustomPlugin") {
              id = "customPlugin"
              implementationClass = "CustomPlugin"
          }
      }
  }
  repositories {
      mavenCentral()
      google()
      jcenter()
  }
  
  dependencies {
      // this cuase a compile error -&gt; implementation("com.android.tools.build:gradle:${constants.Versions.buildTools}")
      implementation("com.android.tools.build:gradle:4.0.0")
      implementation("org.jetbrains.kotlin:kotlin-gradle-plugin:1.3.72")
  
      /* Depend on the default Gradle API's since we want to build a custom plugin */
      implementation(gradleApi())
      implementation(localGroovy())
  }
  </code></pre>