libmain/progress-bar: erase all lines of the multi-line format

When the multi-line log format is enabled, the progress bar usually occupies
multiple lines on the screen. When stopping the progress bar, only the last
line was wiped, leaving all others visible on the screen. Erase all lines
belonging to the progress bar to prevent these leftovers.
Asking the user for input is theoretically affected by a similar issue, but
this is not observed in practice since the only place where the user is asked
(whether configuration options coming from flakes should be accepted) does not
actually have multiple lines on the progress bar. However, there is no real
reason to not fix this either, so let's do it anyway.

Change-Id: Iaa5a701874fca32e6f06d85912835d86b8fa7a16

src/libmain/progress-bar.cc

@@ -92,7 +92,7 @@ void ProgressBar::resume()
             nextWakeup = draw(*state, {});
             state.wait_for(quitCV, std::chrono::milliseconds(50));
         }
-        writeLogsToStderr("\r\e[K");
+        eraseProgressDisplay(*state);
     });
 }
 
@@ -558,7 +558,8 @@ std::optional<char> ProgressBar::ask(std::string_view msg)
 {
     auto state(state_.lock());
     if (state->paused > 0 || !isatty(STDIN_FILENO)) return {};
-    std::cerr << fmt("\r\e[K%s ", msg);
+    eraseProgressDisplay(*state);
+    std::cerr << msg;
     auto s = trim(readLine(STDIN_FILENO));
     if (s.size() != 1) return {};
     draw(*state, {});