Configure Kotlin plugin support for Eclipse in Gradle build

This commit configures the Kotlin plugin for Eclipse in the
spring-core-coroutines Gradle project so that users no longer have to
manually "Configure Kotlin / Add Kotlin Nature" within the Eclipse IDE
after importing projects.

This change is currently limited to the spring-core-coroutines project
since it is the only project in which Java code depends on compiled
Kotlin code; however, this change may later be applied to additional
projects if desirable.

spring-core-coroutines/spring-core-coroutines.gradle

@@ -7,3 +7,13 @@ dependencies {
 	compile("org.jetbrains.kotlinx:kotlinx-coroutines-core:${coroutinesVersion}")
 	compile("org.jetbrains.kotlinx:kotlinx-coroutines-reactor:${coroutinesVersion}")
 }
+
+eclipse.project {
+	buildCommand "org.jetbrains.kotlin.ui.kotlinBuilder"
+	buildCommand "org.eclipse.jdt.core.javabuilder"
+	natures "org.jetbrains.kotlin.core.kotlinNature"
+	natures "org.eclipse.jdt.core.javanature"
+	linkedResource name: "kotlin_bin", type: "2", locationUri: "org.jetbrains.kotlin.core.filesystem:/" + project.name + "/kotlin_bin"
+}
+
+eclipse.classpath.containers "org.jetbrains.kotlin.core.KOTLIN_CONTAINER"