Always clear RX buffer on CTRL-C

Some serial sources clear their RX buffers and others didn't. This
cause CP to skip into the REPL based on characters typed before the
CTRL-C. The serial file transfer code looks for "press any key"
which is skipped in this case.

Fixes circuitpython/web-editor#238

ports/espressif/common-hal/_bleio/CharacteristicBuffer.c

@@ -26,6 +26,7 @@ void bleio_characteristic_buffer_extend(bleio_characteristic_buffer_obj_t *self,
         for (uint16_t i = 0; i < len; i++) {
             if (data[i] == mp_interrupt_char) {
                 mp_sched_keyboard_interrupt();
+                ringbuf_clear(&self->ringbuf);
             } else {
                 ringbuf_put(&self->ringbuf, data[i]);
             }

ports/espressif/supervisor/usb_serial_jtag.c

@@ -46,6 +46,7 @@ static void _copy_out_of_fifo(void) {
     for (size_t i = 0; i < len; ++i) {
         if (rx_buf[i] == mp_interrupt_char) {
             mp_sched_keyboard_interrupt();
+            ringbuf_clear(&ringbuf);
         } else {
             ringbuf_put(&ringbuf, rx_buf[i]);
         }

ports/nordic/common-hal/_bleio/CharacteristicBuffer.c

@@ -29,6 +29,7 @@ static void write_to_ringbuf(bleio_characteristic_buffer_obj_t *self, uint8_t *d
         for (uint16_t i = 0; i < len; i++) {
             if (data[i] == mp_interrupt_char) {
                 mp_sched_keyboard_interrupt();
+                ringbuf_clear(&self->ringbuf);
             } else {
                 ringbuf_put(&self->ringbuf, data[i]);
             }

supervisor/shared/usb/host_keyboard.c

@@ -155,8 +155,9 @@ static void send_bufn_core(const char *buf, size_t n) {
     for (; n--; buf++) {
         int code = *buf;
         if (code == mp_interrupt_char) {
+            ringbuf_clear(&_incoming_ringbuf);
             mp_sched_keyboard_interrupt();
-            return;
+            continue;
         }
         if (ringbuf_num_empty(&_incoming_ringbuf) == 0) {
             // Drop on the floor

supervisor/shared/web_workflow/websocket.c

@@ -227,6 +227,7 @@ void websocket_background(void) {
     while (ringbuf_num_empty(&_incoming_ringbuf) > 0 &&
            _read_next_payload_byte(&c)) {
         if (c == mp_interrupt_char) {
+            ringbuf_clear(&_incoming_ringbuf);
             mp_sched_keyboard_interrupt();
             continue;
         }