Extract FirDiagnosticsCollector to have creation logic in one place

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/diagnostics/collectors/FirDiagnosticsCollector.kt

@@ -0,0 +1,22 @@
+/*
+ * Copyright 2010-2019 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.fir.resolve.diagnostics.collectors
+
+object FirDiagnosticsCollector {
+    fun create(): AbstractDiagnosticCollector {
+        val collector = SimpleDiagnosticsCollector()
+        collector.registerAllComponents()
+        return collector
+    }
+
+    // Use in CLI compiler
+    @Suppress("unused")
+    fun createParallel(): AbstractDiagnosticCollector {
+        val collector = ParallelDiagnosticsCollector(4)
+        collector.registerAllComponents()
+        return collector
+    }
+}

compiler/fir/resolve/tests/org/jetbrains/kotlin/fir/AbstractFirDiagnosticTest.kt

@@ -7,6 +7,7 @@ package org.jetbrains.kotlin.fir
 
 import org.jetbrains.kotlin.fir.declarations.FirFile
 import org.jetbrains.kotlin.fir.resolve.diagnostics.collectors.AbstractDiagnosticCollector
+import org.jetbrains.kotlin.fir.resolve.diagnostics.collectors.FirDiagnosticsCollector
 import org.jetbrains.kotlin.fir.resolve.diagnostics.collectors.ParallelDiagnosticsCollector
 import org.jetbrains.kotlin.fir.resolve.diagnostics.collectors.registerAllComponents
 import org.jetbrains.kotlin.fir.resolve.transformers.FirTotalResolveTransformer
@@ -50,9 +51,6 @@ abstract class AbstractFirDiagnosticsTest : AbstractFirBaseDiagnosticsTest() {
     }
 
     private fun createCollector(): AbstractDiagnosticCollector {
-//        val collector = SimpleDiagnosticsCollector()
-        val collector = ParallelDiagnosticsCollector(4)
-        collector.registerAllComponents()
-        return collector
+        return FirDiagnosticsCollector.create()
     }
 }