Use JavaRegExpHost for Kotlin RegExp injection (KT-15329)

 #KT-15329 Fixed

idea/src/META-INF/injection.xml

 <idea-plugin>
     <extensions defaultExtensionNs="com.intellij">
         <languageInjector implementation="org.jetbrains.kotlin.idea.injection.KotlinLanguageInjector"/>
+
+        <regExpLanguageHost forClass="org.jetbrains.kotlin.psi.KtStringTemplateExpression"
+                            implementationClass="com.intellij.psi.impl.JavaRegExpHost"/>
     </extensions>
 
     <extensions defaultExtensionNs="org.intellij.intelliLang">