Declare shared shadow plugin version and use it consistently

libraries/tools/kotlin-annotation-processing/build.gradle.kts

@@ -8,7 +8,7 @@ buildscript {
     }
 
     dependencies {
-        classpath("com.github.jengelman.gradle.plugins:shadow:1.2.3")
+        classpath("com.github.jengelman.gradle.plugins:shadow:${property("versions.shadow")}")
     }
 }
 

libraries/tools/kotlin-reflect/build.gradle

@@ -8,7 +8,7 @@ buildscript {
     }
     dependencies {
         classpath 'net.sf.proguard:proguard-gradle:5.2.1'
-        classpath 'com.github.jengelman.gradle.plugins:shadow:1.2.4'
+        classpath "com.github.jengelman.gradle.plugins:shadow:${property("versions.shadow")}"
     }
 }
 

libraries/tools/protobuf-lite/build.gradle

@@ -6,7 +6,7 @@ buildscript {
     }
 
     dependencies {
-        classpath 'com.github.jengelman.gradle.plugins:shadow:1.2.4'
+        classpath "com.github.jengelman.gradle.plugins:shadow:${property("versions.shadow")}"
     }
 }