Add pickling of match sub cases

Author: EugeneFlesselle

compiler/src/dotty/tools/dotc/core/tasty/TreePickler.scala

@@ -590,6 +590,7 @@ class TreePickler(pickler: TastyPickler, attributes: Attributes) {
             if (tree.isInline)
               if (selector.isEmpty) writeByte(IMPLICIT)
               else { writeByte(INLINE); pickleTree(selector) }
+            else if tree.isSubMatch then { writeByte(WITH); pickleTree(selector) }
             else pickleTree(selector)
             tree.cases.foreach(pickleTree)
           }

compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala

@@ -1539,6 +1539,9 @@ class TreeUnpickler(reader: TastyReader,
                   readByte()
                   InlineMatch(readTree(), readCases(end))
                 }
+                else if nextByte == WITH then
+                  readByte()
+                  SubMatch(readTree(), readCases(end))
                 else Match(readTree(), readCases(end)))
             case RETURN =>
               val from = readSymRef()

tasty/src/dotty/tools/tasty/TastyFormat.scala

@@ -511,6 +511,7 @@ object TastyFormat {
   final val EMPTYCLAUSE = 45
   final val SPLITCLAUSE = 46
   final val TRACKED = 47
+  final val WITH = 48
 
   // Tree Cat. 2:    tag Nat
   final val firstNatTreeTag = SHAREDterm