Data Inflow: Support grouping by leaf expressions

idea/testData/slicer/inflow/lambdaResult.leafGroups.txt

@@ -0,0 +1,11 @@
+8 val x = foo { <bold>it</bold> }
+8 	val <bold>x = foo { it }</bold>
+8 		val x = <bold>foo { it }</bold>
+3 			fun <bold>foo(f: (Int) -> Int): Int {</bold>
+4 				return <bold>f(1)</bold>
+4 					[LAMBDA] return <bold>f</bold>(1)
+3 						[LAMBDA] fun foo(<bold>f: (Int) -> Int</bold>): Int {
+8 							[LAMBDA] val x = foo <bold>{ it }</bold>
+8 								val x = foo <bold>{ it }</bold>
+8 									val x = foo { <bold>it</bold> }
+