Initial tree-sitter grammar for Dgraph DQL

Skeleton grammar supporting blocks, comments, strings, numbers,
and identifiers. Full DQL keyword support planned for Phase 2.

examples/test.dql

@@ -0,0 +1,18 @@
+# Simple DQL query
+{
+  me(func: eq(name, "Alice")) {
+    name
+    age
+    friend @filter(ge(age, 21)) {
+      name
+    }
+  }
+}
+
+# Mutation example
+{
+  set {
+    _:alice <name> "Alice" .
+    _:alice <age> "30" .
+  }
+}