refactor(#2826): move view to instanced window class (#3153)
* refactor(#2826): singleton View class, WIP
* refactor(#2826): singleton View class, WIP
* refactor(#2826): singleton View class, WIP
* refactor(#2826): singleton View class, WIP
* refactor(#2826): singleton View class, WIP
* refactor(#2826): singleton View class, WIP
* refactor(#2826): singleton View class, WIP
* refactor(#2826): singleton View class
* refactor(#2826): View is an Explorer member
* refactor(#2826): move autocmds to Explorer
* refactor(#2826): API uses Explorer's View
* refactor(#2826): move View into Explorer package
* refactor(#2826): retain necessary view globals
* refactor(#2826): move all winhl to appearance constants
* refactor(#2826): add lifecycle logging to all Explorer members
* refactor(#2826): fix bad cherry-pick
* refactor(#2826): better enumerate_options function
* refactor(#2826): add View.tab_line for debugging
* refactor(#2826): default lifecycle log off
* refactor(#2826): add experimental.multi_instance_debug, split globals out of view, move diagnostics to its own module
* refactor(#2826): instrument View:get_winnr
* refactor(#2826): instrument View:setup_tabpage
* refactor(#2826): instrument View:set_current_win, View:prevent_buffer_override
* refactor(#2826): instrument View:get_bufnr
* refactor(#2826): track member bufnr -> winid with global
* refactor(#2826): tidy experiment names and logs
* vim: nvim-tree: track bufnr via buffer-update channel
* vim: nvim-tree: more logging
* vim: nvim-tree: revert: track bufnr via buffer-update channel
* refactor(#2826): notify error on view winid and bufnr mismatches
* refactor(#2826): notify error on view winid and bufnr mismatches
* refactor(#2826): explorer init logging
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