Move type functions off Context (#4951)

This creates a new check/type.h for most logic, and also moves some
functions to TypeStore in sem_ir/type.h. My approach for TypeStore is to
focus on moving the read-only functions there.

toolchain/check/deduce.cpp

@@ -551,7 +551,8 @@ auto DeductionContext::CheckDeductionIsComplete() -> bool {
       auto param_type_const_id = SubstConstant(
           context(), binding_type_id.AsConstantId(), substitutions_);
       CARBON_CHECK(param_type_const_id.has_value());
-      binding_type_id = context().GetTypeIdForTypeConstant(param_type_const_id);
+      binding_type_id =
+          context().types().GetTypeIdForTypeConstantId(param_type_const_id);
 
       // TODO: Suppress diagnostics here if `diagnose_` is false.
       DiagnosticAnnotationScope annotate_diagnostics(