Minor, refactor bytecode text tests on when-over-string optimization

- Merge `duplicatingItemsSameHashCode.kt` and
  `duplicatingItemsSameHashCode2.kt` into one test enabled on both
  backends, and rename it to
  `duplicatingItemsSameHashCodeFewBranches.kt`.
- Rename `duplicatingItemsSameHashCode3.kt` to
  `duplicatingItemsSameHashCodeMoreBranches.kt`, and also enable it for
  both backends.
- Use JVM_TEMPLATES/JVM_IR_TEMPLATES to check backend-specific behavior:
    1) JVM IR does not optimize less than 2 branches by design
    2) JVM IR does not generate duplicate branches, also by design

Related to KT-36846.

compiler/testData/codegen/bytecodeText/whenStringOptimization/duplicatingItemsSameHashCode.kt

@@ -1,17 +0,0 @@
-// IGNORE_BACKEND: JVM_IR
-// TODO KT-36846 Generate TABLESWITCH/LOOKUPSWITCH in case of matching hashCodes in JVM_IR
-
-fun foo(x : String) : String {
-    assert("abz]".hashCode() == "aby|".hashCode())
-
-    when (x) {
-        "abz]" -> return "abz"
-        "ghi"  -> return "ghi"
-        "aby|" -> return "aby"
-        "abz]" -> return "fail"
-    }
-
-    return "other"
-}
-
-// 1 LOOKUPSWITCH

compiler/testData/codegen/bytecodeText/whenStringOptimization/duplicatingItemsSameHashCodeFewBranches.kt

@@ -1,6 +1,3 @@
-// IGNORE_BACKEND: JVM
-import kotlin.test.assertEquals
-
 fun foo(x : String) : String {
     assert("abz]".hashCode() == "aby|".hashCode())
 
@@ -14,6 +11,9 @@ fun foo(x : String) : String {
     return "other"
 }
 
-// Expecting 0 LOOKUPSWITCH as there is only 2 different hash codes.
-// An IF casecade is more efficient.
+// JVM_TEMPLATES:
+// 1 LOOKUPSWITCH
+
+// JVM_IR_TEMPLATES:
+// Expecting 0 LOOKUPSWITCH as there is only 2 different hash codes. An IF cascade is more efficient.
 // 0 LOOKUPSWITCH

compiler/testData/codegen/bytecodeText/whenStringOptimization/duplicatingItemsSameHashCodeMoreBranches.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND: JVM
 import kotlin.test.assertEquals
 
 fun foo(x : String) : String {
@@ -16,4 +15,6 @@ fun foo(x : String) : String {
 }
 
 // 1 LOOKUPSWITCH
+
+// JVM_IR_TEMPLATES:
 // 0 LDC "fail"