Move some cc classes to their proper place in the file hierarchy

Author: odersky

compiler/src/dotty/tools/dotc/cc/BoxedTypeCache.scala

@@ -0,0 +1,19 @@
+package dotty.tools
+package dotc
+package cc
+
+import core.*
+import Types.*, Symbols.*, Contexts.*
+
+/** A one-element cache for the boxed version of an unboxed capturing type */
+class BoxedTypeCache:
+  private var boxed: Type = compiletime.uninitialized
+  private var unboxed: Type = NoType
+
+  def apply(tp: AnnotatedType)(using Context): Type =
+    if tp ne unboxed then
+      unboxed = tp
+      val CapturingType(parent, refs) = tp: @unchecked
+      boxed = CapturingType(parent, refs, boxed = true)
+    boxed
+end BoxedTypeCache