LUCENE-9077: add a :solr:packaging:dev task that assembles a 'development' image of Solr from which nothing is removed upon consecutive rebuild.

solr/packaging/build.gradle

@@ -25,6 +25,7 @@ plugins {
 
 ext {
   distDir = file("$buildDir/solr-${version}")
+  devDir = file("$buildDir/dev")
 }
 
 configurations {
@@ -108,5 +109,13 @@ task toDir(type: Sync) {
   }
 }
 
+task dev(type: Copy) {
+  description "Assemble Solr distribution into 'development' folder at ${devDir}"
+  group "build"
+
+  from toDir.outputs
+  into devDir
+}
+
 assemble.dependsOn toDir