[Build] Remove BasePluginConvention usages

The entire concept of conventions is deprecated in Gradle. The proposed alternative for `BasePluginConvention` is `BasePluginExtension`
^KTI-1473 In Progress

libraries/tools/kotlin-main-kts/build.gradle.kts

@@ -8,7 +8,7 @@ plugins {
     id("jps-compatible")
 }
 
-val jarBaseName = property("archivesBaseName") as String
+val jarBaseName = the<BasePluginExtension>().archivesName
 
 val localPackagesToRelocate =
     listOf(
@@ -87,7 +87,7 @@ val proguard by task<CacheableProguardTask> {
 
     injars(mapOf("filter" to "!META-INF/versions/**,!kotlinx/coroutines/debug/**"), relocatedJar.get().outputs.files)
 
-    outjars(layout.buildDirectory.file("libs/$jarBaseName-$version-after-proguard.jar"))
+    outjars(layout.buildDirectory.file(jarBaseName.map { "libs/$it-$version-after-proguard.jar" }))
 
     javaLauncher.set(project.getToolchainLauncherFor(JdkMajorVersion.JDK_1_8))