Make local graph execution optional across composed packages

grammar/QuixosCapability.g4

@@ -44,10 +44,15 @@ externalInterfaceDecl
   : EXTERNAL INTERFACE identifier REVISION stringLiteral SEMI
   ;
 
+symbolDecl
+  : SYMBOL identifier ID stringLiteral SEMI
+  ;
+
 resourcePreamble
   : resourceImportDecl
   | externalAtomDecl
   | externalInterfaceDecl
+  | symbolDecl
   | typeAliasDecl
   ;
 
@@ -207,7 +212,7 @@ preparationClause
 
 executionClause
   : EXECUTION REMOTE
-  | EXECUTION (SNAPSHOT | TRANSACTION) TARGETS LBRACK identifierList RBRACK
+  | EXECUTION (SNAPSHOT | TRANSACTION) (TARGETS LBRACK identifierList RBRACK)?
   ;
 
 selectedOperations
@@ -571,6 +576,7 @@ REF: 'ref';
 FRAGMENT: 'fragment';
 IMPORT: 'import';
 EXTERNAL: 'external';
+SYMBOL: 'symbol';
 ATOM: 'atom';
 INTERFACE: 'interface';
 INTERFACES: 'interfaces';