[K/N] Migrate compiler, interop and others to new case conversion api

kotlin-native/Interop/StubGenerator/src/main/kotlin/org/jetbrains/kotlin/native/interop/gen/KotlinCodeModel.kt

@@ -224,12 +224,12 @@ object KotlinTypes {
 
     private open class ClassifierAtPackage(val pkg: String) {
         operator fun getValue(thisRef: KotlinTypes, property: KProperty<*>): Classifier =
-                Classifier.topLevel(pkg, property.name.capitalize())
+                Classifier.topLevel(pkg, property.name.replaceFirstChar(Char::uppercaseChar))
     }
 
     private open class TypeAtPackage(val pkg: String) {
         operator fun getValue(thisRef: KotlinTypes, property: KProperty<*>): KotlinClassifierType =
-                Classifier.topLevel(pkg, property.name.capitalize()).type
+                Classifier.topLevel(pkg, property.name.replaceFirstChar(Char::uppercaseChar)).type
     }
 
     private object BuiltInType : TypeAtPackage("kotlin")

kotlin-native/Interop/StubGenerator/src/main/kotlin/org/jetbrains/kotlin/native/interop/gen/ObjCStubs.kt

@@ -56,7 +56,7 @@ private fun ObjCMethod.getFirstKotlinParameterNameCandidate(forConstructorOrFact
         val selectorPart = this.selector.takeWhile { it != ':' }.trimStart('_')
         if (selectorPart.startsWith("init")) {
             selectorPart.removePrefix("init").removePrefix("With")
-                    .takeIf { it.isNotEmpty() }?.let { return it.decapitalize() }
+                    .takeIf { it.isNotEmpty() }?.let { return it.replaceFirstChar(Char::lowercaseChar) }
         }
     }
 
@@ -69,7 +69,7 @@ private fun ObjCMethod.getKotlinParameters(
 ): List<FunctionParameterStub> {
     if (this.isInit && this.parameters.isEmpty() && this.selector != "init") {
         // Create synthetic Unit parameter, just like Swift does in this case:
-        val parameterName = this.selector.removePrefix("init").removePrefix("With").decapitalize()
+        val parameterName = this.selector.removePrefix("init").removePrefix("With").replaceFirstChar(Char::lowercaseChar)
         return listOf(FunctionParameterStub(parameterName, KotlinTypes.unit.toStubIrType()))
         // Note: this parameter is explicitly handled in compiler.
     }

kotlin-native/Interop/StubGenerator/src/main/kotlin/org/jetbrains/kotlin/native/interop/gen/StubIrElementBuilders.kt

@@ -392,7 +392,7 @@ internal class EnumStubBuilder(
         )
     }
 
-    private fun EnumConstant.isMoreCanonicalThan(other: EnumConstant): Boolean = with(other.name.toLowerCase()) {
+    private fun EnumConstant.isMoreCanonicalThan(other: EnumConstant): Boolean = with(other.name.lowercase()) {
         contains("min") || contains("max") ||
                 contains("first") || contains("last") ||
                 contains("begin") || contains("end")

kotlin-native/Interop/StubGenerator/src/main/kotlin/org/jetbrains/kotlin/native/interop/gen/jvm/CommandLine.kt

@@ -128,7 +128,7 @@ class JSInteropArguments(argParser: ArgParser = ArgParser("jsinterop",
     enum class TargetType {
         WASM32;
 
-        override fun toString() = name.toLowerCase()
+        override fun toString() = name.lowercase()
     }
     val target by argParser.option(ArgType.Choice<TargetType>(),
             description = "wasm target to compile to").default(TargetType.WASM32)