[FIR]: allow char comparison in Fir2Ir

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/Fir2IrVisitor.kt

@@ -1245,6 +1245,7 @@ class Fir2IrVisitor(
             ClassId(FqName("kotlin"), FqName("Int"), false) -> irBuiltIns.intType
             ClassId(FqName("kotlin"), FqName("Float"), false) -> irBuiltIns.floatType
             ClassId(FqName("kotlin"), FqName("Double"), false) -> irBuiltIns.doubleType
+            ClassId(FqName("kotlin"), FqName("Char"), false) -> irBuiltIns.charType
             else -> {
                 return IrErrorCallExpressionImpl(
                     startOffset, endOffset, booleanType, "Comparison of arguments with unsupported type: $classId"

compiler/testData/codegen/box/binaryOp/compareBoxedChars.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 fun <T> id(x: T) = x
 
 fun box(): String {

compiler/testData/codegen/box/primitiveTypes/kt4251.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 fun box(): String {
     val a: Char? = 'a'
     val result = a!! < 'b'