Include ts_tree_copy in wasm build

Fixes #846

lib/binding_web/exports.json

@@ -79,6 +79,7 @@
   "_ts_query_predicates_for_pattern",
   "_ts_query_string_count",
   "_ts_query_string_value_for_id",
+  "_ts_tree_copy",
   "_ts_tree_cursor_current_field_id_wasm",
   "_ts_tree_cursor_current_node_id_wasm",
   "_ts_tree_cursor_current_node_is_missing_wasm",

lib/binding_web/test/tree-test.js

@@ -323,6 +323,31 @@ describe("Tree", () => {
       assert(!cursor.gotoParent());
     })
   });
+
+  describe(".copy", () => {
+    it("creates another tree that remains stable if the original tree is edited", () => {
+      input = 'abc + cde';
+      tree = parser.parse(input);
+      assert.equal(
+        tree.rootNode.toString(),
+        "(program (expression_statement (binary_expression left: (identifier) right: (identifier))))"
+      );
+
+      const tree2 = tree.copy();
+      ([input, edit] = spliceInput(input, 3, 0, '123'));
+      assert.equal(input, 'abc123 + cde');
+      tree.edit(edit);
+
+      const leftNode = tree.rootNode.firstChild.firstChild.firstChild;
+      const leftNode2 = tree2.rootNode.firstChild.firstChild.firstChild;
+      const rightNode = tree.rootNode.firstChild.firstChild.lastChild;
+      const rightNode2 = tree2.rootNode.firstChild.firstChild.lastChild;
+      assert.equal(leftNode.endIndex, 6)
+      assert.equal(leftNode2.endIndex, 3)
+      assert.equal(rightNode.startIndex, 9)
+      assert.equal(rightNode2.startIndex, 6)
+    });
+  });
 });
 
 function spliceInput(input, startIndex, lengthRemoved, newText) {