Capitalize/decapitalize only ASCII characters across project

Use {de,}capitalizeAsciiOnly and to{Lower,Upper}CaseAsciiOnly where
possible, and stdlib's functions with Locale.US everywhere else.

Otherwise, if the default system locale is Turkish, the capital latin
letter "I" is transformed in toLowerCase to "ı" (see
https://github.com/JetBrains/kotlin/blob/66bc142f92085047a1ca64f9a291f0496e33dd98/libraries/stdlib/jvm/test/text/StringJVMTest.kt#L119),
which for example breaks the codegen for `intArrayOf` in
KT-25400/KT-43405.

Similarly, lower case latin letter "i" is transformed to "İ".

 #KT-13631 Fixed
 #KT-25400 Fixed
 #KT-43405 Fixed

compiler/fir/tree/src/org/jetbrains/kotlin/fir/FirRenderer.kt

@@ -27,6 +27,7 @@ import org.jetbrains.kotlin.fir.types.*
 import org.jetbrains.kotlin.fir.visitors.FirVisitorVoid
 import org.jetbrains.kotlin.name.SpecialNames
 import org.jetbrains.kotlin.types.Variance
+import org.jetbrains.kotlin.util.capitalizeDecapitalize.toLowerCaseAsciiOnly
 import org.jetbrains.kotlin.utils.Printer
 import org.jetbrains.kotlin.utils.addToStdlib.safeAs
 
@@ -226,7 +227,7 @@ class FirRenderer(builder: StringBuilder, private val mode: RenderMode = RenderM
     }
 
     private fun FirMemberDeclaration.modalityAsString(): String {
-        return modality?.name?.toLowerCase() ?: run {
+        return modality?.name?.toLowerCaseAsciiOnly() ?: run {
             if (this is FirCallableMemberDeclaration<*> && this.isOverride) {
                 "open?"
             } else {
@@ -343,7 +344,7 @@ class FirRenderer(builder: StringBuilder, private val mode: RenderMode = RenderM
         declaration.renderPhaseIfNeeded()
         print(
             when (declaration) {
-                is FirRegularClass -> declaration.classKind.name.toLowerCase().replace("_", " ")
+                is FirRegularClass -> declaration.classKind.name.toLowerCaseAsciiOnly().replace("_", " ")
                 is FirTypeAlias -> "typealias"
                 is FirSimpleFunction -> "fun"
                 is FirProperty -> {