kotlin: redirect plugin marker resolution to maven artifacts (#176)

The ESRP-backed ADO publish environment uses an internal Maven mirror (Azure Artifacts feed) that doesn't sync the tiny `<plugin-id>.gradle.plugin` marker POMs the Gradle Plugin Portal uses to redirect to real artifacts. Result: `./gradlew check` fails with 'Plugin [id: org.jetbrains.kotlin.jvm, version: 2.3.21] was not found' even though kotlin-gradle-plugin is in the mirror.

Add a pluginManagement.resolutionStrategy.eachPlugin block that maps the Kotlin and Vanniktech plugin IDs directly to their Maven coordinates, bypassing the marker artifact entirely. GHA still resolves via plugin portal normally.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: connor4312

clients/kotlin/settings.gradle.kts

@@ -3,6 +3,23 @@ pluginManagement {
         gradlePluginPortal()
         mavenCentral()
     }
+    // Redirect Gradle plugin marker requests to the actual Maven
+    // coordinates so plugin resolution works even when the build
+    // environment's Maven mirror (e.g. an internal Azure Artifacts feed
+    // used by ESRP-backed publish runs) doesn't have the tiny
+    // `<plugin-id>.gradle.plugin` redirect POMs synced. The real
+    // artifacts live in mavenCentral and are always mirrored.
+    resolutionStrategy {
+        eachPlugin {
+            when (requested.id.id) {
+                "org.jetbrains.kotlin.jvm",
+                "org.jetbrains.kotlin.plugin.serialization" ->
+                    useModule("org.jetbrains.kotlin:kotlin-gradle-plugin:${requested.version}")
+                "com.vanniktech.maven.publish" ->
+                    useModule("com.vanniktech:gradle-maven-publish-plugin:${requested.version}")
+            }
+        }
+    }
 }
 
 dependencyResolutionManagement {