refactor: Add a generic provider module

In preperation for coc support

lua/symbols-outline/providers/nvim-lsp.lua

@@ -0,0 +1,35 @@
+local config = require('symbols-outline.config')
+
+local M = {}
+
+local function getParams()
+    return {textDocument = vim.lsp.util.make_text_document_params()}
+end
+
+-- probably change this
+function M.should_use_provider(bufnr)
+    local clients = vim.lsp.buf_get_clients(bufnr)
+    local ret = false
+
+    for id, client in ipairs(clients) do
+        if config.is_client_blacklisted(id) then
+           goto continue
+        else
+            if client.server_capabilities.documentSymbolProvider then
+               ret = true
+               break
+            end
+        end
+        ::continue::
+    end
+
+    return ret
+end
+
+---@param on_symbols function
+function M.request_symbols(on_symbols)
+    vim.lsp.buf_request_all(0, "textDocument/documentSymbol", getParams(),
+                            on_symbols)
+end
+
+return M