Enable JVM IR by default if language version is >= 1.5

#KT-44021 Fixed

compiler/testData/cli/jvm/jvmIrByDefault.kt

@@ -0,0 +1,13 @@
+// This test checks that with -language-version 1.4 we're using the old JVM backend,
+// and with -language-version 1.5 -- the new JVM IR backend.
+// JVM IR doesn't produce classes for local functions, so the test checks which backend
+// is used by asserting that the file for the anonymous class does or doesn't exist.
+
+// Feel free to remove both _1_4 and _1_5 tests as soon as either the old JVM backend
+// or LV 1.4 is removed, whichever happens earlier.
+
+class C {
+    fun test() {
+        fun local() {}
+    }
+}

compiler/testData/cli/jvm/jvmIrByDefault1_4.args

@@ -0,0 +1,5 @@
+$TESTDATA_DIR$/jvmIrByDefault.kt
+-d
+$TEMP_DIR$
+-language-version
+1.4

compiler/testData/cli/jvm/jvmIrByDefault1_4.out

@@ -0,0 +1 @@
+OK

compiler/testData/cli/jvm/jvmIrByDefault1_4.test

@@ -0,0 +1 @@
+// EXISTS: C$test$1.class

compiler/testData/cli/jvm/jvmIrByDefault1_5.args

@@ -0,0 +1,5 @@
+$TESTDATA_DIR$/jvmIrByDefault.kt
+-d
+$TEMP_DIR$
+-language-version
+1.5

compiler/testData/cli/jvm/jvmIrByDefault1_5.out

@@ -0,0 +1,2 @@
+warning: language version 1.5 is experimental, there are no backwards compatibility guarantees for new language and library features
+OK

compiler/testData/cli/jvm/jvmIrByDefault1_5.test

@@ -0,0 +1 @@
+// ABSENT: C$test$1.class