Multi Instance: Refactor: Move actions/tree/modifiers/expand.lua To Explorer, DirectoryNode and FileNode

[alex-courtis]

• Multi Instance - Contributors Wanted - Please Take An Issue #2255

Important: there is a naming conflict with the existing Explorer:expand method. Rename it to expand_dir_node first.

These expand operations apply to a directory therefore they should be moved into DirectoryNode:

• expand_node should be a public method :expand
• Other functions above should be private methods
• opts used in setup should be replaced by self.explorer.opts

Functions M.all and M.node should be moved to Explorer methods expand_all and expand_node
Explorer:expand_node should just call expand on the node - the appropriate Node method will be used.

A method expand should be added to Node, which will call expand on its parent, if it exists, replacing this logic:

nvim-tree.lua/lua/nvim-tree/actions/tree/modifiers/expand.lua

Line 158 in 1b876db

expand_node(node:is(FileNode) and node.parent or node:as(DirectoryNode), expand_opts)