fix: prompt_prefix leading whitespace normal mode cc (#2699)

* fix: `prompt_prefix` leading whitespace normal mode cc

* [docgen] Update doc/telescope.txt
skip-checks: true

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Co-authored-by: Github Actions <actions@github>
(cherry picked from commit b543aaa)

lua/telescope/pickers.lua

@@ -1509,7 +1509,10 @@ end
 
 --- Get the prompt text without the prompt prefix.
 function Picker:_get_prompt()
-  return vim.api.nvim_buf_get_lines(self.prompt_bufnr, 0, 1, false)[1]:sub(#self.prompt_prefix + 1)
+  local cursor_line = vim.api.nvim_win_get_cursor(self.prompt_win)[1] - 1
+  return vim.api
+    .nvim_buf_get_lines(self.prompt_bufnr, cursor_line, cursor_line + 1, false)[1]
+    :sub(#self.prompt_prefix + 1)
 end
 
 function Picker:_reset_highlights()