init: Signal m_tip_block_cv on Ctrl-C

Signal m_tip_block_cv when Ctrl-C is pressed or SIGTERM is received, the same
way it is currently signalled when the `stop` RPC is called. This lets RPC
calls like `waitforblockheight` and IPC calls like `waitTipChanged` be
interrupted, instead of waiting for their original timeouts and delaying
shutdown.

Historical notes:

- The behavior where `stop` RPC signals `m_tip_block_cv`, but CTRL-C does not,
  has been around since the condition variable was introduced in #30409
  (7eccdaf160).
- The signaling was later moved without changing behavior in #30967
  (5ca28ef28b). This commit moves it again to
  the Interrupt() function, which is probably the place it should have been
  added initially, so it works for Ctrl-C shutdowns as well as `stop`
  shutdowns.
- A Qt shutdown bug calling wait methods was fixed previously in #18452
  (da73f1513a), and this change updates that
  fix to avoid the hang happening again in Qt.

src/node/interfaces.cpp

@@ -132,7 +132,6 @@ public:
     }
     void appShutdown() override
     {
-        Interrupt(*m_context);
         Shutdown(*m_context);
     }
     void startShutdown() override
@@ -141,12 +140,7 @@ public:
         if (!(Assert(ctx.shutdown_request))()) {
             LogError("Failed to send shutdown signal\n");
         }
-
-        // Stop RPC for clean shutdown if any of waitfor* commands is executed.
-        if (args().GetBoolArg("-server", false)) {
-            InterruptRPC();
-            StopRPC();
-        }
+        Interrupt(*m_context);
     }
     bool shutdownRequested() override { return ShutdownRequested(*Assert(m_context)); };
     bool isSettingIgnored(const std::string& name) override