Lock stdin to send and recieve escape sequences

[NSPC911]

Currently, Textual has its driver automatically create a thread to continuously read from stdin.
This means that when you want to send and receive an escape sequence for checking a protocol's availability, you have to do it before the app initialises, causing a bit of lag due to eager loading.

Suggestion: Implement a threading.Lock in textual.app.App that can be used as a context manager to prevent the thread from stealing stdin

Example:

from textual.app import App
from rich.console import Console

console = Console()

class Application(App):
    def on_mount(self) -> None:
        with self.stdin_lock():
            with console.capture() as capture:
                console.print("<seq>")
            str_output = capture.get()

[willmcgugan]

What protocol are you checking for?

[NSPC911]

Specifically, the drag and drop protocol, but I think this would be useful for something like https://github.com/lnqs/textual-image because it eagerly checks for the terminal support