feat(api): add tree.is_visible, tree.is_tree_buf (#2150)

* feat(api): add api.tree.is_visible

* feat(api): add api.tree.is_tree_buf

doc/nvim-tree-lua.txt

@@ -1408,6 +1408,28 @@ tree.toggle_hidden_filter()
 tree.toggle_help()                          *nvim-tree-api.tree.toggle_help()*
     Toggle help view.
 
+tree.is_tree_buf({bufnr})                   *nvim-tree-api.tree.is_tree_buf()*
+    Checks if a buffer is an nvim-tree.
+
+    Parameters: ~
+      • {bufnr} (number|nil) buffer handle, 0 or nil for current buffer
+
+    Return: ~
+      (boolean) buffer is an nvim-tree buffer
+
+tree.is_visible({opts})                      *nvim-tree-api.tree.is_visible()*
+    Checks if nvim-tree is visible on the current, specified or any tab.
+
+    Parameters: ~
+      • {opts} (table) optional parameters
+
+    Options: ~
+      • {tabpage}     (number)  as per |nvim_get_current_tabpage()|
+      • {any_tabpage} (boolean) visible on any tab, default false
+
+    Return: ~
+      (boolean) nvim-tree is visible
+
 ==============================================================================
  5.2 API FILE SYSTEM                                        *nvim-tree-api.fs*