Add hidden file and directory filter option toggle to grep_string

[seffradev]

Description

Add option hidden for toggling if hidden files and directories should appear when running grep_string from builtin.files.

Fixes #3453

Type of change

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

How Has This Been Tested?

local telescope = require "telescope"
local builtin = require "telescope.builtin"

vim.keymap.set("n", "<space>fg", function()
  builtin.grep_string {
    search = vim.fn.input "grep: ",
    hidden = true,
  }
end, { desc = "Grep files in current working directory" })

After running <space>fg and typing a string to grep for in a directory containing hidden objects, they appear. Likewise, commenting out the hidden = true, the hidden files and directories do not appear.

Configuration:

• Neovim version (nvim --version):

NVIM v0.11.0-dev-1315+g668d2569b4
Build type: RelWithDebInfo
LuaJIT 2.1.1732813678

• Operating system and version:

OS: Arch linux
Kernel: 6.13.8-arch1-1

Checklist:

• My code follows the style guidelines of this project (stylua)
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (lua annotations)