[nimsuggest] return the type when on symbol in let/var (#19639)

- make sure `suggestSym` is called after `PSym.typ` is set.

nimsuggest/tests/tdef_let.nim

@@ -0,0 +1,7 @@
+discard """
+$nimsuggest --tester $file
+>def $1
+def;;skLet;;tdef_let.intVar;;int;;$file;;7;;4;;"";;100
+"""
+
+let int#[!]#Var = 10