Try to handle underscores in Parse.parse_in_context

Expose and use the `ctxt_absyn_to_preterm` function created in HOL-Theorem-Prover@ba1eb9a

Aims to fix HOL-Theorem-Prover#1489

Author: hrutvik

src/parse/Parse.sml

@@ -460,11 +460,14 @@ fun smashErrm m =
     | errormonad.Some (_, result) => result
 val stdprinters = SOME(term_to_string,type_to_string)
 
+fun ctxt_absyn_to_preterm fvs a =
+  TermParse.ctxt_absyn_to_preterm (term_grammar()) fvs a
+
 fun parse_in_context FVs q =
   let
     open errormonad
     val m =
-        (q |> Absyn |> absyn_to_preterm) >-
+        (q |> Absyn |> ctxt_absyn_to_preterm FVs) >-
         TermParse.ctxt_preterm_to_term stdprinters NONE FVs
   in
     smashErrm m

src/parse/TermParse.sig

@@ -16,6 +16,7 @@ sig
   val preterm : grammar -> tygrammar -> term quotation -> preterm in_env
   val typed_preterm : grammar -> tygrammar -> hol_type -> term quotation ->
                       preterm in_env
+  val ctxt_absyn_to_preterm : grammar -> term list -> absyn -> preterm in_env
   val absyn_to_preterm : grammar -> absyn -> preterm in_env
   val absyn_to_preterm_in_env : grammar -> absyn -> Parse_support.preterm_in_env
   val absyn_to_term : pprinters -> grammar -> absyn -> term