Re-introduce AssemblyFlagsDeclaration from v2 to v0/v1 (#659)

Follow-up to #653, I didn't notice this was not defined in v0/v1 before
as well

crates/solidity/inputs/language/definition/06-yul/01-assembly-block/productions.yml

@@ -8,15 +8,20 @@
       - optional:
           reference: "AsciiStringLiteral" # label: "evmasm"
       - optional:
-          delimitedBy:
-            open:
-              reference: "OpenParen"
-            parser:
-              reference: "AssemblyFlagsList"
-            close:
-              reference: "CloseParen"
+          reference: "AssemblyFlagsDeclaration"
       - reference: "YulBlock"
 
+- name: "AssemblyFlagsDeclaration"
+  kind: "Parser"
+  unversioned:
+    delimitedBy:
+      open:
+        reference: "OpenParen"
+      parser:
+        reference: "AssemblyFlagsList"
+      close:
+        reference: "CloseParen"
+
 - name: "AssemblyFlagsList"
   kind: "Parser"
   unversioned:

crates/solidity/inputs/language/src/dsl.rs

@@ -185,7 +185,9 @@ slang_grammar! {
 
         parser AssemblyFlagsList = (AsciiStringLiteral separated by Comma) ;
 
-        parser AssemblyStatement = (AssemblyKeyword (AsciiStringLiteral ?) ((AssemblyFlagsList delimited by OpenParen and CloseParen) ?) YulBlock) ;
+        parser AssemblyStatement = (AssemblyKeyword (AsciiStringLiteral ?) (AssemblyFlagsDeclaration ?) YulBlock) ;
+
+        parser AssemblyFlagsDeclaration = (AssemblyFlagsList delimited by OpenParen and CloseParen) ;
 
         inline parser AssignmentOperator = (
             Equal | BarEqual | PlusEqual | MinusEqual | CaretEqual | SlashEqual | PercentEqual | AsteriskEqual | AmpersandEqual |