Data Inflow: Support grouping by leaf expressions

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

@@ -0,0 +1,12 @@
+8 fun bar(<bold>n: Int</bold>) = n
+9 	val <bold>x = foo(::bar)</bold>
+9 		val x = <bold>foo(::bar)</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 {
+9 							[LAMBDA] val x = foo(<bold>::bar</bold>)
+8 								fun <bold>bar(n: Int) = n</bold>
+8 									fun bar(n: Int) = <bold>n</bold>
+8 										fun bar(<bold>n: Int</bold>) = n
+