Replace return with nop to avoid merging line instructions (KT-18949)

Dex ignores subsequent line numbers for same instructions and interprets
instruction after inline as if they were inlined. This makes debugger
behaves as if there's nowhere to stop on line with breakpoint.

This also makes stepping through inline function consistent with
non-inline analog. In both context debugger now stops on '}'.

 #KT-18949 Fixed
 #KT-17120 Fixed

compiler/testData/codegen/bytecodeText/forLoop/loopVarInterval.kt

@@ -6,4 +6,4 @@ fun f() {
 
 // 1 ISTORE 0\s+L3
 // 1 ILOAD 0\s+INVOKEVIRTUAL java/io/PrintStream.print \(C\)V
-// 1 LOCALVARIABLE c C L3 L6 0
+// 1 LOCALVARIABLE c C L3 L7 0