FIR resolve bench: make possible building FIR files via light tree

compiler/fir/lightTree/src/org/jetbrains/kotlin/fir/lightTree/LightTree2Fir.kt

@@ -21,7 +21,7 @@ import java.io.File
 import java.nio.file.Path
 
 class LightTree2Fir(
-    private val session: FirSession = object : FirSessionBase(null) {},
+    val session: FirSession = object : FirSessionBase(null) {},
     private val stubMode: Boolean = false
 ) {
     //private val ktDummyFile = KtFile(SingleRootFileViewProvider(PsiManager.getInstance(project), LightVirtualFile()), false)

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

@@ -11,6 +11,7 @@ import org.jetbrains.kotlin.fir.declarations.FirFile
 import org.jetbrains.kotlin.fir.diagnostics.FirStubDiagnostic
 import org.jetbrains.kotlin.fir.expressions.FirFunctionCall
 import org.jetbrains.kotlin.fir.expressions.FirQualifiedAccessExpression
+import org.jetbrains.kotlin.fir.lightTree.LightTree2Fir
 import org.jetbrains.kotlin.fir.references.FirErrorNamedReference
 import org.jetbrains.kotlin.fir.resolve.firProvider
 import org.jetbrains.kotlin.fir.resolve.impl.FirProviderImpl
@@ -20,6 +21,7 @@ import org.jetbrains.kotlin.fir.visitors.FirTransformer
 import org.jetbrains.kotlin.psi.KtFile
 import org.jetbrains.kotlin.psi.psiUtil.startOffset
 import org.jetbrains.kotlin.utils.addToStdlib.sumByLong
+import java.io.File
 import java.io.PrintStream
 import kotlin.math.max
 import kotlin.reflect.KClass
@@ -111,6 +113,26 @@ class FirResolveBench(val withProgress: Boolean) {
         }
     }
 
+    fun buildFiles(
+        builder: LightTree2Fir,
+        files: List<File>
+    ): List<FirFile> {
+        return files.map { file ->
+            val before = vmStateSnapshot()
+            var firFile: FirFile? = null
+            val time = measureNanoTime {
+                firFile = builder.buildFirFile(file)
+                (builder.session.firProvider as FirProviderImpl).recordFile(firFile!!)
+            }
+            val after = vmStateSnapshot()
+            val diff = after - before
+            recordTime(builder::class, diff, time)
+            firFile!!
+        }.also {
+            totalTime = timePerTransformer.values.sumByLong { it.time }
+        }
+    }
+
     private fun recordTime(stageClass: KClass<*>, diff: VMCounters, time: Long) {
         timePerTransformer.computeIfAbsent(stageClass) { Measure() }.apply {
             this.time += time