[Gradle] Replace deprecated String::capitalize with capitalizeAsciiOnly

This should prevent issues when ascii characters are uppercased or
lowercased on users machines with their locales.

For example in Turkish locale:
* 'i' uppercases to 'İ'
* 'I' lowercases to 'ı'

^KT-38712 Verification Pending

libraries/tools/kotlin-gradle-plugin-api/src/common/kotlin/org/jetbrains/kotlin/gradle/plugin/KotlinJsCompilerType.kt

@@ -5,6 +5,8 @@
 
 package org.jetbrains.kotlin.gradle.plugin
 
+import java.util.*
+
 enum class KotlinJsCompilerType {
     LEGACY,
     IR,
@@ -33,5 +35,5 @@ fun String.removeJsCompilerSuffix(compilerType: KotlinJsCompilerType): String {
         return truncatedString
     }
 
-    return removeSuffix(compilerType.lowerName.capitalize())
+    return removeSuffix(compilerType.lowerName.capitalize(Locale.ENGLISH))
 }