Change the way values work

Change the parsing for values to make them more reusable, in particular
for when I implement extensions.

blueprintcompiler/language/contexts.py

@@ -0,0 +1,28 @@
+# contexts.py
+#
+# Copyright 2023 James Westman <james@jwestman.net>
+#
+# This file is free software; you can redistribute it and/or modify it
+# under the terms of the GNU Lesser General Public License as
+# published by the Free Software Foundation; either version 3 of the
+# License, or (at your option) any later version.
+#
+# This file is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public
+# License along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+# SPDX-License-Identifier: LGPL-3.0-or-later
+
+import typing as T
+from dataclasses import dataclass
+from .common import *
+
+
+@dataclass
+class ValueTypeCtx:
+    value_type: T.Optional[GirType]
+    binding_error: T.Optional[CompileError] = None