refactor: Move buffer/window creation to its own module

For now we have some stuff out of that module to prevent infinite
require loops (set_keymaps/clear_state), but once state goes into its
own module as well then we can work it all into view.lua

lua/symbols-outline/view.lua

@@ -0,0 +1,48 @@
+local config = require('symbols-outline.config')
+
+local M = {}
+
+---creates the outline window and sets it up
+---@return string bufnr
+---@return string bufnr
+function M.setup_view()
+    -- create a scratch unlisted buffer
+    local bufnr = vim.api.nvim_create_buf(false, true)
+
+    -- delete buffer when window is closed / buffer is hidden
+    vim.api.nvim_buf_set_option(bufnr, "bufhidden", "delete")
+
+    local current_win = vim.api.nvim_get_current_win()
+    local current_win_width = vim.api.nvim_win_get_width(current_win)
+
+    -- create a split
+    vim.cmd(config.get_split_command())
+    -- resize to a % of the current window size
+    vim.cmd("vertical resize " ..
+                math.ceil(current_win_width * config.get_width_percentage()))
+
+    -- get current (outline) window and attach our buffer to it
+    local winnr = vim.api.nvim_get_current_win()
+    vim.api.nvim_win_set_buf(winnr, bufnr)
+
+    -- window stuff
+    vim.api.nvim_win_set_option(winnr, "number", false)
+    vim.api.nvim_win_set_option(winnr, "relativenumber", false)
+    vim.api.nvim_win_set_option(winnr, "winfixwidth", true)
+    -- buffer stuff
+    vim.api.nvim_buf_set_name(bufnr, "OUTLINE")
+    vim.api.nvim_buf_set_option(bufnr, "filetype", "Outline")
+    vim.api.nvim_buf_set_option(bufnr, "modifiable", false)
+
+    if config.options.show_numbers or config.options.show_relative_numbers then
+        vim.api.nvim_win_set_option(winnr, "nu", true)
+    end
+
+    if config.options.show_relative_numbers then
+        vim.api.nvim_win_set_option(winnr, "rnu", true)
+    end
+
+    return bufnr, winnr
+end
+
+return M