fix: deprecated warnings

[notomo]

Fix: https://github.com/pmizio/typescript-tools.nvim/issues/266

This PR will fix not to use the following deprecated api.

• vim.tbl_add_reverse_lookup()
• vim.tbl_islist()
• vim.lsp.get_active_clients()

📝 https://neovim.io/doc/user/deprecated.html#deprecated-0.10

[krypciak]

Tested and it doesn't seem to cause issues based on my basic testing

[pedro757]

It should be merged!