Reset DeclarationScope::function_ variable after pre-parsing

"--print-scopes" uses the {function_} variable to print the function
name and locals of a function scope. In case of a pre-parsed function,
the function variable of the scope lives in a zone which is nuked after
pre-parsing, while the scope lives on. This leaves the {function_}
variable pointer in the scope in a state where it points to
invalid memory, causing "--print-scopes" to crash.
This CL fixes the crash by properly resetting the {function_}
pointer.

TBR=verwaest@chromium.org

Change-Id: Id24dbb605bec883317f676265a920fe0ca662301
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1776094Reviewed-by: Simon Zünd <szuend@chromium.org>
Commit-Queue: Simon Zünd <szuend@chromium.org>
Auto-Submit: Simon Zünd <szuend@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63513}

src/ast/scopes.cc

@@ -1437,6 +1437,7 @@ void DeclarationScope::ResetAfterPreparsing(AstValueFactory* ast_value_factory,
   sloppy_block_functions_.Clear();
   rare_data_ = nullptr;
   has_rest_ = false;
+  function_ = nullptr;
 
   DCHECK_NE(zone_, ast_value_factory->zone());
   zone_->ReleaseMemory();