[BT] Add support for in-process incremental compilation

#KT-61865 Fixed

build-common/src/org/jetbrains/kotlin/build/sourcesUtils.kt

@@ -5,5 +5,5 @@
 
 package org.jetbrains.kotlin.build
 
-val DEFAULT_KOTLIN_SOURCE_FILES_EXTENSIONS = listOf("kt", "kts")
+val DEFAULT_KOTLIN_SOURCE_FILES_EXTENSIONS = setOf("kt", "kts")
 

build-common/src/org/jetbrains/kotlin/incremental/fileUtils.kt

@@ -22,7 +22,7 @@ import java.io.IOException
 fun File.isJavaFile() =
         extension.equals("java", ignoreCase = true)
 
-fun File.isKotlinFile(sourceFilesExtensions: List<String>): Boolean =
+fun File.isKotlinFile(sourceFilesExtensions: Collection<String>): Boolean =
     !isJavaFile() && sourceFilesExtensions.any { it.equals(extension, ignoreCase = true) }
 
 fun File.isClassFile(): Boolean =