Store file-level annotations in IrFile (should be on some descriptor, really).

compiler/testData/ir/irText/declarations/fileWithAnnotations.kt

@@ -0,0 +1,6 @@
+// WITH_RUNTIME
+@file:JvmName("FileWithAnnotations")
+
+fun foo() {}
+
+val bar = 42

compiler/testData/ir/irText/declarations/fileWithAnnotations.txt

@@ -0,0 +1,8 @@
+FILE /fileWithAnnotations.kt
+  fileAnnotations:
+    @kotlin.jvm.JvmName(name = "FileWithAnnotations")
+  FUN public fun foo(): kotlin.Unit
+    BLOCK_BODY
+  PROPERTY public val bar: kotlin.Int = 42
+    EXPRESSION_BODY
+      CONST Int type=kotlin.Int value='42'