Clear the control-C cancel flag earlier, allowing event handlers to run

When the user presses control-C, fish marks a cancellation signal which
prevents fish script from running, allowing it to properly unwind.
Prior to this commit, the signal was cleared in the reader. However this
missed the case where a binding would set $fish_bind_mode which would
trigger event handlers: the event handlers would be skipped because of
the cancellation flag was still set. This is similar to #6937.

Let's clear the flag earlier, as soon as we it's set, in inputter_t.
Fixes #8125.

tests/pexpects/bind_mode_events.py

@@ -1,5 +1,7 @@
 #!/usr/bin/env python3
 from pexpect_helper import SpawnedProc
+import os
+import signal
 
 sp = SpawnedProc()
 send, sendline, sleep, expect_prompt = sp.send, sp.sendline, sp.sleep, sp.expect_prompt
@@ -33,3 +35,21 @@ sleep(0.050)
 
 send("echo mode changes: $MODE_CHANGES\r")
 expect_prompt("\r\nmode changes: default insert default insert\r\n")
+
+# Regression test for #8125.
+# Control-C should return us to insert mode.
+send("set -e MODE_CHANGES\r")
+expect_prompt()
+
+# Put some text on the command line and then go back to normal mode.
+send("echo stuff")
+sp.expect_str("echo stuff")
+send("\033")
+sleep(0.050)
+
+os.kill(sp.spawn.pid, signal.SIGINT)
+sleep(0.050)
+
+# We should be back in insert mode now.
+send("echo mode changes: $MODE_CHANGES\r")
+expect_prompt("\r\nmode changes: default insert\r\n")