Add Flex component.

PiperOrigin-RevId: 572830650
Change-Id: I6908228087b7b9683be3506c8d9cdc725ed5dcd5

test/xml/xml_native_reader_test.cc

@@ -631,7 +631,7 @@ TEST_F(XMLReaderTest, InvalidSkinGroup) {
   )";
   std::array<char, 1024> error;
   mjModel* model = LoadModelFromString(xml, error.data(), error.size());
-  ASSERT_THAT(model, IsNull());
+  EXPECT_THAT(model, IsNull());
   EXPECT_THAT(
       error.data(),
       HasSubstr("skin group must be between 0 and 5\nElement 'skin', line 7"));

test/xml/xml_native_writer_test.cc

@@ -1062,6 +1062,7 @@ TEST_F(PluginTest, WriteReadCompare) {
         // if file is meant to fail, skip it
         if (absl::StrContains(p.path().string(), "malformed_") ||
             absl::StrContains(p.path().string(), "touch_grid") ||
+            absl::StrContains(p.path().string(), "gmsh_") ||
             absl::StrContains(p.path().string(), "cow")) {
           continue;
         }