feat(providers): Inital COC support

Closes #68
Still needs support for code actions/hover/rename etc

lua/symbols-outline/providers/coc.lua

@@ -0,0 +1,24 @@
+-- local config = require('symbols-outline.config')
+
+local M = {}
+
+-- probably change this
+function M.should_use_provider(_)
+    local coc_installed = vim.fn.exists("*CocActionAsync")
+
+    if not coc_installed then return end
+
+    local coc_attached = vim.fn.call('CocAction', {'ensureDocument'})
+    local has_symbols = vim.fn.call('CocHasProvider', {'documentSymbol'})
+
+    return coc_attached and has_symbols;
+end
+
+---@param on_symbols function
+function M.request_symbols(on_symbols)
+    vim.fn.call('CocActionAsync', {'documentSymbols', function (_, symbols)
+        on_symbols{[1000000]={result=symbols}}
+    end})
+end
+
+return M