Implement context classpath extraction using particular class,...

Use it in the main-kts.
Also improve diagnoistics related to the definition loading.

#KT-26828 fixed (after this commit - finally, see also another related commit)

libraries/scripting/common/src/kotlin/script/experimental/host/configurationFromTemplate.kt

@@ -60,7 +60,7 @@ fun createCompilationConfigurationFromTemplate(
     fun scriptConfigInstance(kclass: KClass<out ScriptCompilationConfiguration>): ScriptCompilationConfiguration = try {
         kclass.objectInstance ?: kclass.createInstance()
     } catch (e: Throwable) {
-        throw IllegalArgumentException(ILLEGAL_CONFIG_ANN_ARG, e)
+        throw IllegalArgumentException("$ILLEGAL_CONFIG_ANN_ARG: ${e.message}", e)
     }
 
     return ScriptCompilationConfiguration(scriptConfigInstance(mainAnnotation.compilationConfiguration)) {

libraries/scripting/jvm/src/kotlin/script/experimental/jvm/jvmScriptCompilation.kt

@@ -6,6 +6,7 @@
 package kotlin.script.experimental.jvm
 
 import java.io.File
+import kotlin.reflect.KClass
 import kotlin.script.experimental.api.*
 import kotlin.script.experimental.host.ScriptingHostConfiguration
 import kotlin.script.experimental.jvm.util.scriptCompilationClasspathFromContext
@@ -22,6 +23,12 @@ open class JvmScriptCompilationConfigurationBuilder : PropertiesCollection.Build
     companion object : JvmScriptCompilationConfigurationKeys
 }
 
+fun JvmScriptCompilationConfigurationBuilder.dependenciesFromClassContext(
+    contextClass: KClass<*>, vararg libraries: String, wholeClasspath: Boolean = false
+) {
+    dependenciesFromClassloader(*libraries, classLoader = contextClass.java.classLoader, wholeClasspath = wholeClasspath)
+}
+
 fun JvmScriptCompilationConfigurationBuilder.dependenciesFromCurrentContext(vararg libraries: String, wholeClasspath: Boolean = false) {
     dependenciesFromClassloader(*libraries, wholeClasspath = wholeClasspath)
 }

libraries/tools/kotlin-main-kts/src/org/jetbrains/kotlin/mainKts/scriptDef.kt

@@ -16,6 +16,7 @@ import kotlin.script.experimental.api.*
 import kotlin.script.experimental.jvm.JvmDependency
 import kotlin.script.experimental.jvm.compat.mapLegacyDiagnosticSeverity
 import kotlin.script.experimental.jvm.compat.mapLegacyScriptPosition
+import kotlin.script.experimental.jvm.dependenciesFromClassContext
 import kotlin.script.experimental.jvm.dependenciesFromCurrentContext
 import kotlin.script.experimental.jvm.jvm
 
@@ -27,9 +28,8 @@ object MainKtsScriptDefinition : ScriptCompilationConfiguration(
     {
         defaultImports(DependsOn::class, Repository::class)
         jvm {
-            dependenciesFromCurrentContext("kotlin-main-kts")
+            dependenciesFromClassContext(MainKtsScriptDefinition::class, "kotlin-main-kts")
         }
-        // variant: dependencies(collectDependenciesFromCurrentContext(...
         refineConfiguration {
             onAnnotations(DependsOn::class, Repository::class, handler = MainKtsConfigurator())
         }