fix(treesitter): fix TSNode:tree() double free (#24796)

Problem: `push_tree`, every time its called for the same TSTree with
`do_copy=false` argument, creates a new userdata for it. Each userdata,
when garbage collected, frees the same TSTree C object.

Solution: Add flag to userdata, which indicates, should C object,
which userdata points to, be freed, when userdata is garbage collected.

test/functional/treesitter/node_spec.lua

@@ -4,6 +4,7 @@ local clear = helpers.clear
 local eq = helpers.eq
 local exec_lua = helpers.exec_lua
 local insert = helpers.insert
+local assert_alive = helpers.assert_alive
 
 before_each(clear)
 
@@ -14,6 +15,17 @@ end
 describe('treesitter node API', function()
   clear()
 
+  it('double free tree', function()
+    insert('F')
+    exec_lua([[
+      vim.treesitter.start(0, 'lua')
+      vim.treesitter.get_node():tree()
+      vim.treesitter.get_node():tree()
+      collectgarbage()
+    ]])
+    assert_alive()
+  end)
+
   it('can move between siblings', function()
     insert([[
       int main(int x, int y, int z) {