StringStreams no longer errors when intialized with literals on arc/orc (#19708)

(cherry picked from commit 26acc97)

Author: beef331

lib/pure/streams.nim

@@ -1271,6 +1271,8 @@ else: # after 1.3 or JS not defined
 
     new(result)
     result.data = s
+    when defined(gcOrc) or defined(gcArc):
+      prepareMutation(result.data) # Allows us to mutate using `addr` logic like `copyMem`, otherwise it errors.
     result.pos = 0
     result.closeImpl = ssClose
     result.atEndImpl = ssAtEnd

tests/stdlib/tstreams.nim

@@ -74,3 +74,5 @@ block:
   doAssert(ss.peekLine(str))
   doAssert(str == "uick brown fox jumped over the lazy dog.")
   doAssert(ss.getPosition == 5) # haven't moved
+  ss.setPosition(0) # Ensure we dont error with writing over literals on arc/orc #19707
+  ss.write("hello")