fixes #26094; memory leak on exception unwinding — raising proc's res… (#26100)

…ult is never destroyed

fixes #26094



Conceptually, the new lowering for `destination = raisingCall()` is:

```nim
var tmp: T
try:
  tmp = raisingCall()
  let value = tmp
  wasMoved(tmp)
  destination = value
finally:
  destroy(tmp)
```
So whether `raisingCall` Succeeds or not, `tmp` is destroyed

---------

Co-authored-by: Andreas Rumpf <rumpf_a@web.de>

tests/arc/t23267_result.nim

@@ -0,0 +1,67 @@
+discard """
+  valgrind: true
+  cmd: "nim c -d:useMalloc $file"
+  matrix: "--mm:arc; --mm:orc"
+  disabled: "freebsd"
+  disabled: "osx"
+  disabled: "openbsd"
+  disabled: "windows"
+  disabled: "32bit"
+"""
+
+import std/options
+
+type Foo = object
+  id: string
+  items: seq[string]
+
+proc build(x: int): Foo =
+  result = Foo(id: "padding-padding", items: @["a", "b", "c"])
+  if x < 0:
+    raise newException(ValueError, "boom")
+
+proc parseResult(x: int): Foo =
+  try:
+    result = build(x)
+  except CatchableError:
+    result = default(Foo)
+
+proc parseVar(x: int; dst: var Foo): bool =
+  dst = build(x)
+  result = true
+
+proc parseOption(x: int): Option[Foo] =
+  result = some(build(x))
+
+const iterations = 10_000
+
+doAssert parseResult(1).items == @["a", "b", "c"]
+
+var successfulDst: Foo
+doAssert parseVar(1, successfulDst)
+doAssert successfulDst.id == "padding-padding"
+
+doAssert parseOption(1).get.items == @["a", "b", "c"]
+
+var unchangedDst = Foo(id: "old", items: @["old"])
+try:
+  discard parseVar(-1, unchangedDst)
+except CatchableError:
+  discard
+doAssert unchangedDst == Foo(id: "old", items: @["old"])
+
+for _ in 0 ..< iterations:
+  discard parseResult(-1)
+
+for _ in 0 ..< iterations:
+  var dst: Foo
+  try:
+    discard parseVar(-1, dst)
+  except CatchableError:
+    discard
+
+for _ in 0 ..< iterations:
+  try:
+    discard parseOption(-1)
+  except CatchableError:
+    discard