Add ray-x/lsp_signature.nvim plugin

Improves the built-in signature help UI, enables toggling of signatures,
and displays multiple signatures when available.

lua/plugins/completions.lua

@@ -18,6 +18,7 @@ return {
     'j-hui/fidget.nvim',
     'folke/trouble.nvim',
     'nvim-tree/nvim-web-devicons',
+    'ray-x/lsp_signature.nvim',
 
     -- Lua vim module support in lua language server
     'folke/neodev.nvim',
@@ -186,7 +187,6 @@ return {
         -- |vim.lsp.buf.hover()| if the server supports it, unless
         -- |'keywordprg'| was customized before calling |vim.lsp.start()|.
         vim.keymap.set('n', 'K', vim.lsp.buf.hover, opts)
-        vim.keymap.set('i', '<C-h>', vim.lsp.buf.signature_help, opts)
 
         -- Format whole buffer mapping
         vim.keymap.set('n', '<leader>gq', vim.lsp.buf.format, opts)
@@ -218,5 +218,12 @@ return {
     vim.keymap.set('n', '<leader>tr', function()
       require('trouble').toggle()
     end, { remap = false })
+    require('lsp_signature').setup({
+      floating_window = true,
+      hint_enable = false,
+      toggle_key = '<C-h>',
+      toggle_key_flip_floatwin_setting = true,
+      select_signature_key = '<C-l>',
+    })
   end
 }