Ruby/Rust/QL: move databaseMetadata to prefix.dbscheme

This has no effect on ruby.dbscheme, and adds the relation to
ql.dbscheme and rust.dbscheme. (The relation will be required for
overlay support).

Author: nickrolfe

ql/ql/src/ql.dbscheme

@@ -108,6 +108,12 @@ yaml_locations(unique int locatable: @yaml_locatable ref,
 
 @yaml_locatable = @yaml_node | @yaml_error;
 
+/*- Database metadata -*/
+databaseMetadata(
+  string metadataKey: string ref,
+  string value: string ref
+);
+
 /*- QL dbscheme -*/
 @ql_add_expr_left_type = @ql_add_expr | @ql_aggregate | @ql_call_or_unqual_agg_expr | @ql_comp_term | @ql_conjunction | @ql_disjunction | @ql_expr_annotation | @ql_if_term | @ql_implication | @ql_in_expr | @ql_instance_of | @ql_literal | @ql_mul_expr | @ql_negation | @ql_par_expr | @ql_prefix_cast | @ql_qualified_expr | @ql_quantified | @ql_range | @ql_set_literal | @ql_special_call | @ql_super_ref | @ql_unary_expr | @ql_variable
 

ql/ql/src/ql.dbscheme.stats

@@ -22436,5 +22436,41 @@
                 </dep>
             </dependencies>
         </relation>
+        <relation>
+            <name>databaseMetadata</name>
+            <cardinality>1</cardinality>
+            <columnsizes>
+                <e>
+                    <k>metadataKey</k>
+                    <v>1</v>
+                </e>
+                <e>
+                    <k>value</k>
+                    <v>1</v>
+                </e>
+            </columnsizes>
+            <dependencies>
+                <dep>
+                    <src>metadataKey</src>
+                    <trg>value</trg>
+                    <val>
+                        <hist>
+                            <budget>12</budget>
+                            <bs/>
+                        </hist>
+                    </val>
+                </dep>
+                <dep>
+                    <src>value</src>
+                    <trg>metadataKey</trg>
+                    <val>
+                        <hist>
+                            <budget>12</budget>
+                            <bs/>
+                        </hist>
+                    </val>
+                </dep>
+            </dependencies>
+        </relation>
         </stats>
 </dbstats>