gql: suppress -Wextra warnings in generated ANTLR parser

The generated GQLParser.cpp carries Sempred methods whose _localctx
parameter is unused (they delegate to precpred(_ctx, ...)). Under the
parent repo's CI (ENABLE_WERROR=1 / -Werror) these produced
-Werror=unused-parameter build failures for the gql extension.

Mirror how the parent handles its generated ANTLR code (cypher_parser
is silenced by -Wno-extra in third_party/CMakeLists.txt): disable
-Wextra-only warnings for the generated parser/lexer/visitor OBJECT
target. Hand-written gql code is unaffected; -no-visitor/-no-listener
does not help since Sempred methods are always generated.

Also vendor the Apache-2.0 opengql/grammar (GQL.g4 @ 1.9.0) under
third_party/opengql so scripts/generate_gql_grammar.cmake works from a
fresh clone and the grammar revision is pinned. Regeneration from the
vendored grammar is byte-identical to the checked-in generated files.

Author: adsharma

gql/src/parser/CMakeLists.txt

@@ -5,6 +5,18 @@ add_library(lbug_gql_extension_parser
         GQLParser.cpp
         GQLVisitor.cpp)
 
+# The generated ANTLR parser/lexer/visitor are warning-clean under -Wall but, like
+# the parent repo's generated ANTLR code (see third_party/antlr4_cypher, which is
+# silenced by -Wno-extra in the parent's third_party/CMakeLists.txt), they declare
+# parameters that -Wextra flags as unused (e.g. the `_localctx` argument of the
+# generated Sempred methods, which delegate to precpred(_ctx, ...)). Those become
+# hard errors when the parent CI builds extensions with ENABLE_WERROR=1 / -Werror.
+# Mirror the parent's treatment of generated code: disable the -Wextra-only warnings
+# for this generated-object target only. Hand-written gql code is unaffected.
+if(NOT MSVC)
+    target_compile_options(lbug_gql_extension_parser PRIVATE -Wno-extra)
+endif()
+
 set(GQL_EXTENSION_OBJECT_FILES
         ${GQL_EXTENSION_OBJECT_FILES} $<TARGET_OBJECTS:lbug_gql_extension_parser>
         PARENT_SCOPE)