Apply common configuration to custom publications in kotlin-test

To do that, extract parts of publishing setup into reusable functions.
This change makes signing and repository configuration applied to all
project publications, not just to the Main one.

Also:
- Get rid of dependencies from non-default variants in the root pom
- Add an empty javadoc jar

KT-40225

libraries/kotlin.test/build.gradle.kts

@@ -1,9 +1,14 @@
 import org.jetbrains.kotlin.gradle.plugin.KotlinPlatformType
+import plugins.configureDefaultPublishing
+import plugins.configureKotlinPomAttributes
+import groovy.util.Node
+import groovy.util.NodeList
 
 plugins {
     `kotlin-multiplatform` apply false
     base
     `maven-publish`
+    signing
 }
 
 open class ComponentsFactoryAccess
@@ -248,42 +253,56 @@ val annotationsMetadataComponent = componentFactory.adhoc("annotations-common").
     }
 }
 
+val emptyJavadocJar by tasks.creating(Jar::class) {
+    archiveClassifier.set("javadoc")
+}
 
+configureDefaultPublishing()
 
 publishing {
     publications {
         create("main", MavenPublication::class) {
             from(rootComponent)
             artifact(combinedSourcesJar)
-            // TODO: Remove all optional dependencies from root pom
+            // Remove all optional dependencies from the root pom
+            pom.withXml {
+                val dependenciesNode = (asNode().get("dependencies") as NodeList).filterIsInstance<Node>().single()
+                val optionalDependencies = (dependenciesNode.get("dependency") as NodeList).filterIsInstance<Node>().filter {
+                    ((it.get("optional") as NodeList).singleOrNull() as Node?)?.text() == "true"
+                }
+                optionalDependencies.forEach { dependenciesNode.remove(it) }
+            }
+            configureKotlinPomAttributes(project, "Kotlin Test Multiplatform library")
         }
         jvmTestFrameworks.forEach { framework ->
             create(framework, MavenPublication::class) {
                 artifactId = "kotlin-test-$framework"
                 from(components[framework])
                 artifact(tasks.getByPath(":kotlin-test:kotlin-test-$framework:sourcesJar") as Jar)
+                configureKotlinPomAttributes(project, "Kotlin Test Support for $framework")
             }
         }
         create("js", MavenPublication::class) {
             artifactId = "kotlin-test-js"
             from(jsComponent)
             artifact(tasks.getByPath(":kotlin-test:kotlin-test-js:sourcesJar") as Jar)
+            configureKotlinPomAttributes(project, "Kotlin Test for JS")
         }
         create("common", MavenPublication::class) {
             artifactId = "kotlin-test-common"
             from(commonMetadataComponent)
             artifact(tasks.getByPath(":kotlin-test:kotlin-test-common:sourcesJar") as Jar)
+            configureKotlinPomAttributes(project, "Kotlin Test Common")
         }
         create("annotationsCommon", MavenPublication::class) {
             artifactId = "kotlin-test-annotations-common"
             from(annotationsMetadataComponent)
             artifact(tasks.getByPath(":kotlin-test:kotlin-test-annotations-common:sourcesJar") as Jar)
+            configureKotlinPomAttributes(project, "Kotlin Test Common")
+        }
+        withType<MavenPublication> {
+            suppressAllPomMetadataWarnings()
+            artifact(emptyJavadocJar)
         }
     }
 }
-
-tasks {
-    val install by creating {
-        dependsOn(publishToMavenLocal)
-    }
-}