Avoid requiring `it` parameter in Kotlin bean DSL

By using function literals with receiver, we can avoid requiring
lambda parameters for a shorter and nicer syntax. Based on a
proposal from Joseph Taylor.

Issue: SPR-15815

spring-context/src/main/kotlin/org/springframework/context/support/BeanDefinitionDsl.kt

@@ -89,7 +89,7 @@ open class BeanDefinitionDsl(val condition: (ConfigurableEnvironment) -> Boolean
 									  isLazyInit: Boolean? = null,
 									  isPrimary: Boolean? = null,
 									  isAutowireCandidate: Boolean? = null,
-									  crossinline function: (BeanDefinitionContext) -> T) {
+									  crossinline function: BeanDefinitionContext.() -> T) {
 		
 		val customizer = BeanDefinitionCustomizer { bd ->
 			scope?.let { bd.scope = scope.name.toLowerCase() }
@@ -122,7 +122,7 @@ open class BeanDefinitionDsl(val condition: (ConfigurableEnvironment) -> Boolean
 	 * Take in account bean definitions enclosed in the provided lambda only when the
 	 * specified environment-based predicate is true.
 	 */
-	fun environment(condition: (ConfigurableEnvironment) -> Boolean, init: BeanDefinitionDsl.() -> Unit): BeanDefinitionDsl {
+	fun environment(condition: ConfigurableEnvironment.() -> Boolean, init: BeanDefinitionDsl.() -> Unit): BeanDefinitionDsl {
 		val beans = BeanDefinitionDsl(condition::invoke)
 		beans.init()
 		children.add(beans)

spring-context/src/test/kotlin/org/springframework/context/support/BeanDefinitionDslTests.kt

@@ -32,8 +32,8 @@ class BeanDefinitionDslTests {
 		val beans = beans { 
 			bean<Foo>()
 			bean<Bar>("bar", scope = Scope.PROTOTYPE)
-			bean { Baz(it.ref<Bar>()) }
-			bean { Baz(it.ref("bar")) }
+			bean { Baz(ref()) }
+			bean { Baz(ref("bar")) }
 		}
 
 		val context = GenericApplicationContext()
@@ -55,8 +55,8 @@ class BeanDefinitionDslTests {
 				profile("pp") {
 					bean<Foo>()
 				}
-				bean { Baz(it.ref<Bar>()) }
-				bean { Baz(it.ref("bar")) }
+				bean { Baz(ref()) }
+				bean { Baz(ref("bar")) }
 			}
 		}
 
@@ -78,10 +78,10 @@ class BeanDefinitionDslTests {
 		val beans = beans {
 			bean<Foo>()
 			bean<Bar>("bar")
-			bean { FooFoo(it.env["name"]) }
-			environment({it.activeProfiles.contains("baz")}) {
-				bean { Baz(it.ref()) }
-				bean { Baz(it.ref("bar")) }
+			bean { FooFoo(env["name"]) }
+			environment( { activeProfiles.contains("baz") } ) {
+				bean { Baz(ref()) }
+				bean { Baz(ref("bar")) }
 			}
 		}