K2: fix NSME on toChar for subclasses of Number

Code in `ReplaceNumberToCharCallSitesLowering` relies on `Number.toChar`
being declared in IR as non-abstract. Otherwise the
`resolveFakeOverride` call there doesn't work, and the lowering can't
rewrite the call to `toInt().toChar()`, and we end up with a call to the
missing method `Number.toChar` in the bytecode.

 #KT-57217 Fixed

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

@@ -77,9 +77,10 @@ class IrBuiltInsOverFir(
 
     private val number by createClass(kotlinIrPackage, IdSignatureValues.number, build = { modality = Modality.ABSTRACT }) {
         configureSuperTypes()
-        for (targetPrimitive in primitiveIrTypesWithComparisons) {
+        for (targetPrimitive in primitiveNumericIrTypes) {
             createMemberFunction("to${targetPrimitive.classFqName!!.shortName().asString()}", targetPrimitive, modality = Modality.ABSTRACT)
         }
+        createMemberFunction("toChar", charType, modality = Modality.OPEN)
         finalizeClassDefinition()
     }
     override val numberClass: IrClassSymbol get() = number.klass

compiler/testData/codegen/box/primitiveTypes/numberToChar/javaSubclass.kt

@@ -2,9 +2,6 @@
 // ISSUE: KT-23447
 // WITH_STDLIB
 
-// IGNORE_BACKEND_K2: JVM_IR
-// Ignore reason: KT-57217
-
 // FILE: MyNumber.java
 
 public class MyNumber extends Number {

compiler/testData/ir/irText/stubs/constFromBuiltins.__kotlin.Int.fir.ir.txt

@@ -22,7 +22,7 @@ CLASS IR_EXTERNAL_DECLARATION_STUB CLASS name:Int modality:FINAL visibility:publ
     annotations:
       IntrinsicConstEvaluation
     overridden:
-      public abstract fun toChar (): kotlin.Char declared in kotlin.Number
+      public open fun toChar (): kotlin.Char declared in kotlin.Number
     $this: VALUE_PARAMETER name:$this type:kotlin.Int
   FUN BUILTIN_CLASS_METHOD name:toByte visibility:public modality:OPEN <> ($this:kotlin.Int) returnType:kotlin.Byte
     annotations: