Restore original variable name mangling for captured/receiver $this

Design for the new one is still not finished.

compiler/testData/checkLocalVariablesTable/underscoreNames.kt

@@ -28,7 +28,7 @@ fun box() {
 // VARIABLE : NAME=c TYPE=C INDEX=9
 // VARIABLE : NAME=a TYPE=D INDEX=7
 // VARIABLE : NAME=this TYPE=LUnderscoreNamesKt$box$1; INDEX=0
-// VARIABLE : NAME=$dstr$x$-0024_-0024$y TYPE=LA; INDEX=1
+// VARIABLE : NAME=$dstr$x$_u24__u24$y TYPE=LA; INDEX=1
 // VARIABLE : NAME=$noName_1 TYPE=Ljava/lang/String; INDEX=2
 // VARIABLE : NAME=w TYPE=I INDEX=3
 // VARIABLE : NAME=x TYPE=D INDEX=4