Tab char ' '(\t) displays as ^I when pasting into input

[huangyxi]

In some downstream applications, we want to paste code directly into the input. If a tab character is included in the code, the prompt displays it as ^I.

For a specific instance, when coding in an R script in VSCode, the "vscode-R" extension could send a block of code into the REPL of the Python package radian, which utilizes prompt-toolkit as the IO in the REPL. If the block of code contains tabs, the REPL will display abnormally. randy3k/radian#313

Thankfully, reproducing this behavior is not a hard task.

1. Make a simple prompt:

>>> from prompt_toolkit import prompt
>>> prompt("Input: ")
Input: 

2. Paste tab char > <, resulting in:

Input: tab char >^I<

I have tried a solution mentioned in tmbo/questionary#154 (comment), which patches prompt_toolkit.layout.screen .Char.display_mappings['\t'] = '\t', and a solution in Issue #1452, which listens for the tab key to insert spaces. However, it still does not work properly. I also found a workaround mentioned in Issue #556, but it is not suitable in our situation.