IJ file type optimizations based on extension

#KTIJ-21668

Merge-request: KT-MR-6288
Merged-by: Vladimir Dolzhenko <Vladimir.Dolzhenko@jetbrains.com>

compiler/cli/src/org/jetbrains/kotlin/cli/jvm/compiler/KotlinCoreEnvironment.kt

@@ -314,7 +314,7 @@ class KotlinCoreEnvironment private constructor(
     private val VirtualFile.javaFiles: List<VirtualFile>
         get() = mutableListOf<VirtualFile>().apply {
             VfsUtilCore.processFilesRecursively(this@javaFiles) { file ->
-                if (file.fileType == JavaFileType.INSTANCE) {
+                if (file.extension == JavaFileType.DEFAULT_EXTENSION || file.fileType == JavaFileType.INSTANCE) {
                     add(file)
                 }
                 true

compiler/cli/src/org/jetbrains/kotlin/cli/jvm/compiler/TopDownAnalyzerFacadeForJVM.kt

@@ -310,7 +310,7 @@ object TopDownAnalyzerFacadeForJVM {
         // 'isDirectory' check is needed because otherwise directories such as 'frontend.java' would be recognized
         // as Java source files, which makes no sense
         override fun contains(file: VirtualFile) =
-            file.fileType === JavaFileType.INSTANCE && !file.isDirectory
+            (file.extension == JavaFileType.DEFAULT_EXTENSION || file.fileType === JavaFileType.INSTANCE) && !file.isDirectory
 
         override fun toString() = "All Java sources in the project"
     }

compiler/cli/src/org/jetbrains/kotlin/cli/jvm/compiler/coreEnvironmentUtils.kt

@@ -58,7 +58,7 @@ inline fun List<KotlinSourceRoot>.forAllFiles(
             continue
         }
 
-        if (!vFile.isDirectory && vFile.fileType != KotlinFileType.INSTANCE) {
+        if (!vFile.isDirectory && vFile.extension != KotlinFileType.EXTENSION && vFile.fileType != KotlinFileType.INSTANCE) {
             configuration.report(CompilerMessageSeverity.ERROR, "Source entry is not a Kotlin file: $sourceRootPath", reportLocation)
             continue
         }