fix #11354 jsgen not carefully handle genAddr with nkHiddenAddr,nkStm… (#15078)

* fix #11354 jsgen not carefully handle genAddr with nkHiddenAddr,nkStmtListExpr; genAsgn with lvalue tyVar and rvalue tyPtr

* correct logic

* add test for #11354

* handle nkHiddenAddr when n.len == 1

* Update compiler/jsgen.nim

* Update compiler/jsgen.nim

* Apply suggestions from code review

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

tests/js/t11354.nim

@@ -0,0 +1,20 @@
+discard """
+  output: '''
+0
+@[@[0, 1]]
+'''
+"""
+
+type
+  TrackySeq[T] = object
+    s: seq[T]
+    pos: int
+
+proc foobar(ls: var TrackySeq[seq[int]], i: int): var seq[int] =
+  echo ls.pos  # removing this, or making the return explicit works
+  ls.s[i]
+
+var foo: TrackySeq[seq[int]]
+foo.s.add(@[0])
+foo.foobar(0).add(1)
+echo foo.s