feat: set filter input filetype to NvimTreeFilter

[wsdjeg]

can not disable nvim-cmp in nvimtree filter buffer, with this PR:

cmp.setup({
    enabled = function()
        if vim.bo.filetype == 'NvimTreeFilter'  then
            return false
        end
        return true
    end
    ----
}）

[alex-courtis]

Works nicely for 0.11 and 0.10, many thanks!

Please

• add help
• resolve style issue

[wsdjeg]

@alex-courtis thank, changes have been done.

[alex-courtis]

Many thanks for your contribution!