Fuzzer fixes (#940)

* better handling of container_decl_arg_trailing

* ignore semantic token when moving backwards

* use custom ast functions instead of from std

tests/lsp_features/semantic_tokens.zig

@@ -32,6 +32,18 @@ test "semantic tokens - comments" {
     // TODO more tests
 }
 
+test "semantic tokens - string literals" {
+    // https://github.com/zigtools/zls/issues/921
+    try testSemanticTokens(
+        \\"
+        \\"",// 
+        \\"": 
+    ,
+        // no idea if this output is correct but at least it doesn't crash
+        &.{ 1, 3, 3, 8, 0, 1, 0, 2, 4, 0, 0, 0, 2, 9, 0 },
+    );
+}
+
 const file_uri = switch (builtin.os.tag) {
     .windows => "file:///C:/test.zig",
     else => "file:///test.zig",